The Premier League's "big four" meet on Sunday in what has been billed as the most significant day of the season so far.
Adding extra spice to the weekend is the fact that, with Manchester United at Liverpool and Arsenal hosting Chelsea, the two fixtures pit traditional local rivals against each other.
BBC Sport looks at who is in the best shape ahead of the weekend and how significant the fixtures are likely to be in the race for the title.
TIGHT AT THE TOP
As we approach the halfway point in the season all of the big four remain firmly in the hunt for the Premier League title.
The same could not be said over recent years.
You have to go back to the 2002-03 season to find a season when the big four were more tightly grouped at this stage of the year.
Reigning champions Manchester United made their best start to a Premier League season last year, losing just one of their first 16 games - at home to Arsenal on 17 September.
606: DEBATE
Yet by this stage of the season last year United had amassed 44 points - eight more than this year - and ensured that two of the big four were effectively out of the running for the title.
Arsenal might have won at Old Trafford but as they took to the field to play Portsmouth on 16 December they trailed United by 15 points, while Liverpool were 16 behind Sir Alex Ferguson's team.
Five years ago, just five points separated the big four, with Liverpool the lowest placed in fifth on 31 points.
Gerard Houllier's team had led the table at the start of December but lost three straight games to slip down from the summit with Arsenal replacing them at the top.
This year there are seven points between the top four, led once again by Arsenal.
Liverpool, in fourth place, have a game in hand on their opponents.
However, if Rafael Benitez's side were to lose to United and Chelsea beat Arsenal then Liverpool would end the weekend seven points adrift of third, putting them in increasing danger of losing ground in the race for the title.
If Liverpool lose and Arsenal beat Chelsea, the Reds would find themselves 10 points behind the leaders.
RECENT FORM AND HEAD-TO-HEADS
Liverpool slipped up at Reading last Saturday, losing 3-1, but otherwise their recent form has been excellent.
The reverse at the Madejski Stadium was their first Premier League defeat of the season and the Reds had won their three previous top-flight fixtures.
LIVERPOOL v MAN UTD Anfield, Premier Lge
Furthermore, the victory over Marseille in the Champions League on Wednesday ensured Liverpool's progress from the group stage of that competition and considerably eased the pressure on boss Benitez.
His team have not been short of goals either. Since drawing 0-0 at Ewood Park on 3 November they have found the net 26 times in their last seven games in all competitions.
However, Liverpool have not managed to beat Manchester United in a Premier League fixture at Anfield since November 2001.
Manchester United have won four and drawn the other of their five visits to Liverpool since, with John O'Shea scoring a last-minute winner last March as the Red Devils closed in on the title.
United will be encouraged by the fact that although Liverpool are unbeaten in the league at Anfield this season, they have won just three of their seven games, drawing the other four.
ARSENAL v CHELSEA Highbury/Emirates, Premier Lge
However, United's two league defeats this season have come away from Old Trafford, at the hands of local rivals Manchester City and Bolton.
Chelsea are unbeaten at Arsenal in three seasons and travel to the Emirates Stadium with Avram Grant's team in good form.
Israeli Grant was named boss of Chelsea on 20 September and tasted defeat in his first game, at Manchester United.
Since then Chelsea are unbeaten in 16 games in all competitions and chief executive Peter Kenyon recently commented that Grant had "exceeded people's expectations".
Arsenal boss Arsene Wenger will be looking for a response from his team after last Sunday's loss at lowly Middlesbrough - their first Premier League defeat of the season.
The Gunners have been extremely strong at home, winning seven and drawing one of their eight Premier League games at the Emirates.
THE STATE OF THE SQUADS
Arsenal boss Wenger is currently the hardest hit by injuries of the big four with midfielders Alexander Hleb, Mathieu Flamini and, significantly, Cesc Fabregas all out, although the Spaniard could return on Sunday.
Wenger has used 20 players in the Premier League so far, with Kolo Toure and Gael Clichy the only two players to have started every fixture.
BIG FOUR TOP SCORERS
Striker Emmanuel Adebayor is the league's joint top scorer along with Manchester United's Ronaldo. Both have nine goals.
Fabregas is Arsenal's second-top scorer with six goals, while fit-again Robin Van Persie has five. Without them the Gunners have been heavily reliant on Adebayor's goals.
Frank Lampard and Didier Drogba are the top joint scorers for Chelsea in the league with five goals each.
Drogba misses the trip to Arsenal following surgery - leaving Grant with a sizeable hole to fill.
Drogba's goal tally has come from 10 starts and one substitute appearance.
The other three strikers - Andriy Shevchenko, Claudio Pizarro and Salomon Kalou - have managed six goals in a combined total of 17 starts and 17 appearances off the bench.
MOST APPEARANCES FROM TOP FOUR IN PREMIER LEAGUE
Liverpool boss Benitez has been heavily criticised for his rotation policy, with some arguing he should play his strongest team more often.
But leading striker Fernando Torres has started the last five games in all competitions and is in prime form, as his goal against Marseille in midweek demonstrated.
Four Liverpool players have spent more than 1,000 minutes on the pitch in the Premier League this season, in contrast to eight from Sunday's opponents United.
The evergreen Ryan Giggs, Ronaldo and Carlos Tevez have featured extensively for Manchester United but it is with his defensive selection that Ferguson has been particularly consistent.
Rio Ferdinand has started all 16 games, while Edwin van der Sar, Patrice Evra and Wes Brown have started 15, with Nemanja Vidic on 14.
Perhaps as a consequence of this continuity, United have the meanest defence in the top flight, having conceded eight goals in 16 games.
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