Varndell played a crucial part in Leicester's fine second-half display
Harlequins (6) 13
Pens: Malone 2
Leicester (10) 42
Leicester winger Tom Varndell scored a fine hat-trick as the Tigers cruised to a bonus-point victory at the Stoop.
Tries: Varndell 3, Croft 2
Cons: Goode 4
Pens: Goode 2
Drops: G Murphy
Harlequins went 6-0 ahead but the Tigers hit back when Varndell collected Andy Goode's cute chip to score.
Leicester came out firing after the break and Tom Croft finished off a fine counter to put his side in control.
Varndell raced in from deep inside his own half for a superb solo try before claiming a third, while Quins scored a consolation through David Strettle.
Leicester's comprehensive victory took them to third in the Premiership and will serve as a warning to their rivals that they are in no mood to surrender the title after a stuttering campaign so far.
And it was also a perfect response to the comments of Harlequins coach Dean Richards, who cheekily hinted in the build-up to the match that all is not well at his old club under new boss Marcelo Loffreda.
Varndell was only recalled to the starting XV after outside centre Dan Hipkiss pulled out with a groin injury, with Ollie Smith moving in from the wing to the number 13 shirt.
The home side, who themselves lost number eight Nick Easter before kick-off, made the early running and fly-half Chris Malone kicked them in front with two penalties in the opening 18 minutes.
But the Tigers started to get back into the game and after Goode put his side on the board with a penalty, Varndell judged his run perfectly to catch Goode's deft chip and score under the posts.
Although Leicester were not at their fluent best in the opening period, the visitors cut loose after the break.
To implode as we did in the 20 minutes after half-time is unacceptable
Harlequins boss Dean Richards
Ireland full-back Geordan Murphy struck an opportunistic drop-goal to set his side on the way and after Goode added a second penalty, Croft crossed in the corner following a wonderful counter-attack led by returning skipper Martin Corry.
And Varndell will have alerted England's selectors with a superb second straight from the Quins restart.
Varndell leapt to claim the high ball 30m from his own line and, after breaking through a gap, put on the gas to leave the home defence for dead.
Although Quins never stopped coming forward, they could not break the Leicester defence and Croft added his second after collecting a pinpoint cross-field kick from Goode.
Varndell grabbed his hat-trick after All Blacks centre Aaron Mauger took advantage of some dreadful tackling to offload, and although Strettle did manage to just power his way over late on, it was only a consolation.
Harlequins rugby director Dean Richards:
"Tom Croft is an outstanding talent. I think he is a really good player.
"He has everything. He might lack a little experience but you could throw him into the England team and I don't think it would hurt them at all.
"For us, there are very few positives we can take out of today. We knew we would be up against it but to implode as we did in the 20 minutes after half-time is unacceptable."
Leicester coach Marcelo Loffreda on Tom Varndell:
"Tom was very good. He was man of the match today and he has everything he needs to be a top player in his position.
"He is really working very hard to build his consistency and his concentration and he is getting better and better. That is what we are focusing on giving him at the club.
"Concentration in the international arena is the main thing. You can have the talent but if you are not focused in practice and in the preparation you will not perform well."
Harlequins: Brown; Strettle, Barry, Turner-Hall, Monye; Malone, Gomarsall; Jones, Botha, Ross, Kohn, Evans, Robshaw, Skinner, Hala'ufia.
Replacements: Fuga, Nebbett, Percival, Guest, Volley, Jarvis, Keogh.
Leicester: G Murphy; Varndell, O Smith, Mauger, J Murphy; Goode, Laussucq; Ayerza, Kayser, Castrogiovanni, Deacon, Kay, Croft, Moody, Corry (c).
Replacements: Chuter, Young, Hamilton, Deacon, B Youngs, Humphreys, Erinle.