Man Utd 1-0 Middlesbrough
Tottenham 1-2 Chelsea
GOALFLASHES AND MAJOR INCIDENTS (all times GMT)
PLAYER RATER: What do you reckon? Well, as things stand Andrei Shevchenko is the top performer at White Hart Lane with 7.29, closely followed by fellow goalscorer Shaun Wright-Phillips with 7.24.
The top man at Old Trafford is Cristiano Ronaldo with 8.45.
2203: As the Chelsea players celebrate on the pitch, a Tottenham fans runs at them from the stands. Chaos follows before a multitude of stewards defuse the situation in their own particular way. However, it look as though Didier Drogba may have reacted in an aggresive manner before the stewards arrived on the scene.
2203: A mass outbreak of celebrations at White Hart Lane for the Chelsea players and Jose Mourinho. Lots of jumping up and down, while Didier Drogba throws his shirt into the crowd. He still has his gloves on though.
2201: FULL-TIME Tottenham 1-2 Chelsea
The final whistle sounds at White Hart Lane. More disappointment for Tottenham, who should have won the first tie at Stamford Bridge after leading 3-1. Chelsea will now play Blackburn for a place in the final - possibly against Manchester United.
2154: FULL-TIME Manchester United 1-0 Middlesbrough
Cristiano Ronaldo's goal is enough to take United through to the FA Cup semi-finals. Sir Alex Ferguson's team will play Watford for a place in the final.
2153: SENDING OFF
Middlesbrough's James Morrison is awarded a straight red card for a lunge on Cristiano Ronaldo. A fracas ensues, of which Wayne Rooney is a central figure.
2149: Tottenham are pushing for an equaliser. Ricardo Carvalho dangerously opts to leave a low cross - and his gamble pays off when it runs past two Tottenham players.
2146: As time ticks down at Old Trafford, United are dominating with Boro pinned in their own half.
2143: GOAL Tottenham 1-2 Chelsea
Robbie Keane puts Tottenham back into the tie with a coolly taken penalty after Ricardo Carvalho trips the largely mediocre Dimitar Berbatov. Keane tries to pick the ball out of the net but Petr Cech petulantly kicks it away and is booked for his trouble.
2141: Middlesbrough's bench are very unhappy with the penalty awarded against them. They apparently make certain accusations, incensing United assistant boss Carlos Queiroz.
2140: Chelsea are dominating at White Hart Lane. Tottenham are supposed to be chasing the game but have had just 34% of possession over the last 15 minutes.
2120: GOAL Manchester United 1-0 Middlesbrough
Cristiano Ronaldo puts his team ahead from the penalty spot after he is fouled by Jonathan Woodgate. The penalty oozes arrogance as the forward staggers his approach to the ball but the finish is beyond dispute. The ball is placed in the top corner - and the possibility of a Man Utd versus Chelsea final remains very much on.
2133: Andrei Shevchenko is played clean through but wrongly halted by the offside flag. Much gloved finger wagging ensues.
2130: The match at Old Trafford has livened up. Boro started out with two solid defensive banks - or should that be buses - of four, but have shown more ambition the longer the match has gone on. Wayne Rooney misses another good chance - Mark Schwarzer saving from him again.
2129: Jermain Defoe comes on for Steed Malbranque. Chelsea recovered a two-goal deficit at Stamford Bridge - but can Tottenham do the same at their ground?
2120: GOAL Tottenham 0-2 Chelsea
Shaun Wright-Phillips extends Chelsea's lead with another brilliant strike. Didier Drogba chested the ball superbly into Wright-Phillips's path as the little winger cut in from the left flank before demonstrating superb technique to score from a tight angle with his left foot. This time Jose Mourinho leaps around on the touchline.
2120: Intelligent goalkeeping again from Mark Schwarzer as he runs Cristiano Ronaldo wide, leaving the winger with only an acute angle from which to fire in a shot. Fire in he does, but his effort thuds against the post and bounces to safety.
2120: GOAL Tottenham 0-1 Chelsea
Andrei Shevchenko brilliantly puts Chelsea in front, cutting in from the right and working the ball on to his left foot before smashing it home from a tight angle. Remarkable. Does Jose Mourinho celebrate? No, he castigates Ashley Cole for a poor piece of defending minutes earlier.
2118: The crowd have found their voice at White Hart Lane - and with good reason. This FA Cup replay is finally starting to live up to its billing.
2116: A good chance falls to Middlesbrough's Stewart Downing but he misses the target from 12 yards. Boro are enjoying their best spell of the game.
2115: Pascal Chimbonda volleys at goal but does not make a clean contact and Chelsea's superb keeper Petr Cech saves to his left. The tempo has quickened.
2114: Alan Smith is booked for a late challenge on Jonathan Woodgate. Remember Elland Road?
2111: The second half has started at White Hart Lane. How look before we see an attacking change? Not long I hope if the stalemate continues.
2105: The tie at Old Trafford has resumed. No major action to report as yet. United are playing their fourth game in 10 days - will tired legs catch them out in the end?
Cristiano Ronaldo is on absolute fire at the moment. He is fantastic.
BBC pundit Mark Hughes on the Portuguese forward's recent form.
PLAYER RATER: Half-time in both games. Your top performer so far at Old Trafford is, surprise, surprise, Cristiano Ronaldo with an impressive 8.36. Way down the M6 at White Hart Lane, Dimitar Berbatov is top of the pops with 7.74. In truth, though, both ties could do with a little bit of magic to enliven our Monday.
2054: Chelsea end the first half on top, winning a succession of corners. However, the half ends goalless - in stark contrast from the four at Stamford Bridge eight days ago. Can we please have some goals after the break?
2050: Both teams are playing very cagily and patiently.
BBC Sport pundit David Pleat at White Hart Lane
2049: The half-time whistle sounds at Old Trafford. No goals and not much drama - here's hoping for more of both after the break.
2044: Wayne Rooney is played clean through on goal by Ryan Giggs but the United striker is foiled by Boro keeper Mark Schwarzer, who saves at the forward's feet. Rooney had opted to try to round the keeper.
2041: Referee Martin Atkinson books Didier Drogba for dissent. The Ivorian is incensed after being penalised for a foul and slams the ball to the floor in disgust. He is not happy but punished for his petulance.
2038: "We have not seen the physios on the pitch yet. The game at Stamford Bridge has hardly stopped at all but the two goalkeepers have not been seriously troubled."
BBC Sport commentator John Motson
2035: The first yellow card of the evening and the winner is....Lassana Diarra of Chelsea for a challenge on Aaron Lennon. Actually, the Chelsea defender is somewhat unfortunate to have gone into the book, having hardly touched the Spurs forward.
2033: United are still on top in their match with Boro at Old Trafford, while it is very much even steven between Tottenham and Chelsea.
"I think that it will finish 2-2 after 90 minutes at White Hart Lane and then Spurs will win the penalty shoot-out (5-4)."
T_Toon on 606
2024: No early goals in either tie, but not for the want of trying. Shaun Wright-Phillips earns a round of applause from the Chelsea bench after going close from 20 yards.
2018: It has been all Man Utd but Boro striker Mark Viduka's eyes light up as a juicy half-volley drops right in front of him on the edge of the box. He drills it goalwards but it slams into the advertising hoardings a foot wide of the post. A decent chance for the Aussie - Boro's first.
2017: Andrei Shevchenko, increasingly influential, has enjoyed some good early touches - but short shirt sleeves and gloves? Surely the Ukraine striker can handle a reasonably chilly March evening in London.
2012: Dimitar Berbatov almost unlocks the Chelsea defence with a sublime backheel. Michael Ballack then goes close for Chelsea with a low strike. By the way, Ashley Cole is being roundly booed every time he touches the ball. Who did he used to play for?
2008: Wayne Rooney gives Middlesbrough their first scare with a low shot that Jonathan Woodgate does well to block. From the resulting corner Nemanja Vidic towers above the Boro defence and powers a header at Mark Schwarzer. Cristiano Ronaldo shoots wide shortly afterwards. United are quick out of the blocks once again.
2008: Under way at White Hart Lane. Martin Jol, arms folded and chewing furiously, looks on from the sidelines. Jose Mourinho is sporting the look of complete indifference he has mastered so well.
2005: England coach Steve McClaren - after a busy day calling Preston's David Nugent and Aston Villa's Gareth Barry into his latest squad - must be hoping there are no fresh injuries. He is watching from the stands at White Hart Lane.
2003: Blackburn await the winners of Tottenham and Chelsea. Rovers manager Mark Hughes claims he is undecided who he wants to play "It is not an easy choice," said the diplomatic Hughes.
2002: The match between Manchester United and Middlesbrough starts at Old Trafford. Alan Smith is making his first FA Cup appearance since breaking his leg in the game between United and Liverpool at Anfield on 18 February 2006.
1955: I haven't looked forward to a Monday night this much in ages. Don't forget to use the Player Rater - relevant link under the scores at the top - to let us know who you think is having a blinder, or indeed a stinker.
1935: Old Trafford and White Hart Lane are starting to fill as the countdown to kick-off approaches. But what drama lies in store and who will make it through to the semi-final stage?
With the final taking place at the rebuilt Wembley the stakes could not be higher.
Manchester United defender Wes Brown replaces the injured Gary Neville at right-back, while Alan Smith takes over Ryan Giggs' striking responsibilities. Teenage striker Craig Cathcart is among the substitutes, as are fellow youngsters Chris Eagles and Tom Heaton.
Middlesbrough welcome back Jonathan Woodgate and Mark Viduka, who were rested in the weekend defeat to Manchester City. Julio Arca passes a late fitness test to start and Emanuel Pogatetz has shaken off a knee injury to feature in defence.
He's back. Man of the moment Dimitar Berbatov returns to the Tottenham team as do Robbie Keane and Aaron Lennon from the team that defeated Watford on Saturday. Jermain Defoe is a substitute, but there is no place on the bench for Mido.
Chelsea winger Shaun Wright-Phillips is preferred to Arjen Robben, while Lassana Diarra plays at right-back, replacing Khalid Boulahrouz. Mikel Jon Obi returns after a four-match ban but Michael Essien remains sidelined through injury.