|Harlequins (13) 18|
|Tries: Alofa, Ward Cons: N Evans Pens: N Evans, Jackson|
|Leicester Tigers (3) 27|
|Tries: Harrison, Penalty try, Burns Cons: Burns 2, Williams Pens: Burns 2|
Leicester's 24 second-half points ended Harlequins' unbeaten home league record to move level with fourth-placed Bath.
After the ball bounced off the corner flag, Alofa Alofa got the only try before the break as the hosts led 13-3.
Sam Harrison dotted down for Tigers and they were given a penalty try when Adam Thompstone was taken out of the air by Aaron Morris, who was sin-binned.
Freddie Burns added a third when he intercepted to score before Dave Ward grabbed a late Quins consolation try.
Relive Leicester's victory at Harlequins
The visitors had Luke Hamilton yellow-carded prior to Ward's try, but still managed to record their first win away from Welford Road since November.
John Kingston's Quins side had won all seven of their Premiership matches at the Twickenham Stoop this season, but are now 10 points behind Leicester in sixth.
Leicester fly-half Burns, who will join Bath in the summer, scored 15 points to help Aaron Mauger's team over the line.
Tigers wing Thompstone was given a head injury assessment after being illegally felled by Morris, but he was able to continue, but Quins fly-half Nick Evans was forced off on his return from seven weeks out with a shoulder injury.
Harlequins: Morris; Yarde, Marchant, Hopper, Alofa; N Evans, Mulchrone; Lambert, Buchanan, A Jones, Merrick, Matthews, Chisholm, Ward (capt), Luamanu.
Replacements: Gray, O Evans, Shields, South, Naoupu, L Jones, Jackson, Walker.
Leicester: Veainu; Thompstone, Betham, Mermoz, Pietersen; Burns, Harrison; Genge, McGuigan, Bateman, Wells, Barrow (capt), Fitzgerald, O'Connor, McCaffrey.
Replacements: Youngs, Brugnara, Betts, Williams, Hamilton, Kitto, Williams, Smith.
Referee: Dean Richards.
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