Harlequins (9) 26
Tries: Brown, Monye Cons: Evans 2 Pens: Evans 4
Leicester (16) 26
Tries: Murphy, Flood Cons: Flood 2
Pens: Flood 4
Quins wing Tom Williams (left) and Toby Flood compete for a high kick
A last-minute Nick Evans conversion gave Quins a draw against Leicester in front of a record Premiership crowd of 50,000 at Twickenham.
Three Evans penalties, to one from Toby Flood, gave Harlequins a 9-3 lead.
Two Flood penalties and converted tries from Johne Murphy and Tom Croft saw Leicester take a 23-9 advantage.
Mike Brown replied with a converted try for Quins and after a penalty apiece from Flood and Evans, Ugo Monye crossed to set up Evans to clinch the draw.
The 50,000 attendance was the biggest for a single match in the Premiership's regular season, smashing the previous best of 23,709 which London Irish managed when they hosted Wasps earlier this year.
In taking the decision to move the game across the road from the Stoop to Twickenham, London aristocrats Harlequins were no doubt influenced by the success Parisian counterparts Stade Francais have had in taking big matches to the cavernous Stade de France.
Quins beat the French side there in front of nigh-on 80,000 in the Heineken Cup just three weeks ago and on Saturday they wore the sort of pink and blue shirts - in aid of Cancer Research - that notorious peacocks Stade would have felt right at home in.
Evans gave Quins an early lead at a dry but cold Twickenham with a penalty but despite the hosts enjoying the upper hand in the opening stages it was the visitors who came within inches of the opening try.
When a Harlequins attack ran aground the Tigers were given the chance to counter.
At one stage they had a four on two but De Wet Barry made a superb corner-flagging tackle to deny Leicester wing Murphy in the right-hand corner.
From the resulting line-out the midlanders went desperately close to a try once more but hooker Benjamin Kayser was just bundled into touch as he tried to squeeze in by the corner flag.
However, they did leave with some points as Flood landed a penalty, only for Evans to reply in kind after 20-year-old centre Jordan Turner-Hall had featured prominently in a series of Quins attacks.
Flood soon missed a chance to level the scores and things went from bad to worse for the visitors as Kayser was sin-binned for blatant use of hands in the ruck right in front of the referee.
The Tigers had a let-off as Evans missed the resultant penalty but the former New Zealand number 10 soon added his third penalty to give Quins a six-point lead.
Harlequins scrum-half Danny Care tries to evade Martin Corry
However, Quins then lost captain Will Skinner, a former Leicester player, for the same offence as Kayser and while he was in the bin Leicester scored 13 points.
Flood landed two penalties and the Tigers scored their first try right on the half-time whistle.
When Julien Dupuy hacked through Monye failed to gather and Murphy was on hand to kick ahead and dot down, with Flood's conversion giving the Tigers a 16-9 lead at half-time despite Quins enjoying the better of the opening 40 minutes.
It got even better for Leicester 10 minutes into the second half as Murphy escaped up the touchline after a line-out had gone astray and blind-side flanker Croft showed real pace to stride over from 40m.
Flood converted to make it 23-9 but the score stung Quins into life and they hit back as Brown slid out of Flood's tackle to stretch over.
Evans landed the conversion to cut the gap to seven points before Flood missed a penalty after the Tigers splintered the home scrum.
Quins could have pulled level, but Barry's pass failed to go to hand with the line begging after Evans had sliced past Flood to spark a superb attack.
Flood restored Leicester's 10-point margin but Evans once again cut the gap to seven before a barn-storming finish to match the occasion.
Quins conjured a sweeping attack which finished with Monye brushing off replacement Tom Varndell before diving over in the corner.
Evans drilled the conversion between the posts from the touchline and there was still time for a dust-up after the restart as a record-breaking occasion ended in suitably climactic fashion.
Quins boss Dean Richards:
"This is a side which never gives up, a side with a huge amount of character.
"Teams are finding out that we are a difficult nut to crack. There is a resilience that wasn't there last year or the year before."
Quins fly-half Nick Evans:
"I love playing in front of crowds like this and I just knew I had to back my routine and trust my rhythm.
"It is a bit of a hollow feeling. It was really good to get the draw in the end but after the first half we really should have won the game."
Leicester boss Heyneke Meyer on Evans:
"I have always rated Evans as an unbelievable player. I thought he would get the kick because we didn't deserve to win the game and he is a quality player who is good under pressure."
Harlequins: Brown; T Williams, Tiesi, Turner-Hall, Monye; N Evans, Care; Jones, Fuga, Ross, Percival, Robson, Robshaw, Skinner, Easter.
Replacements: Brooker for Fuga (50), J Evans for Percival (66), Guest for Robshaw (72).
Not Used: Lambert, Gomarsall, Barry, Malone.
Sin Bin: Skinner (30).
Leicester: Hamilton; J Murphy, Hipkiss, Mauger, Smith; Flood, Dupuy; Stankovich, Kayser, White, Corry, Wentzel, Croft, Moody, Crane.
Replacements: Varndell for Hamilton (43), Chuter for Kayser (60), Castrogiovanni for White (37), Newby for Crane (67).
Not Used: Herring, B Youngs, Rabeni.
Sin Bin: Kayser (23), Moody (77).
Ref: Dave Pearson (Newcastle).