Leicester coach Dean Richards left it late to add the aces to his pack and give his side a great final chance of qualifying for Europe's Premier Club competition next season.

The double Heineken Cup winners, whose hat-trick was derailed by Munster in this season's quarter-final, looked to have it all to do when they were trailing 23-6.

But Richards introduced England skipper Martin Johnson, Darren Garforth and Dorian West from the bench in the 51st minute - and added Graham Rowntree soon afterwards.

And they provided the momentum to cut the final deficit to three points.

That makes Leicester the big favourites for Sunday's wild card semi-final qualifier second leg at home at Welford Road as they bid for a place in the play-off final at Northampton's Franklin's Gardens on May 31.

After falling 3-0 behind to a 19th minute penalty from Tim Stimpson, Harlequins took full advantage of a sub-standard first-half display by an under-strength Tigers side to lead 17-0 at half-time.

After Stimpson opened the scoring, it took them just a minute to produce the cutting edge which Leicester, with the one exception of Irish star Geordan Murphy, lacked for so much of the match.

Quins had the good fortune to get away with a blatant forward pass from number eight Tony Diprose before England centre Will Greenwood sent hooker Tani Fuga over for the first try.

Six minutes later scrum-half Matt Powell caught the Leicester defence unawares by breaking down the short side from a maul before kicking ahead for centre Mel Deane to snatch the ball out of the air and touch down.

Fly-half Paul Burke converted both and added penalties in the 31st minute and the first minute of the second half to stretch the lead to 20-3.

A Leicester penalty by Stimpson was cancelled out by Burke's eighth drop goal of the season for Harlequins before, in the 51st minute, Richards finally abandoned his game of brinkmanship by introducing Johnson, West and Garforth.

The impact was almost immediate in terms of added impetus although none of the three were involved as Murphy took a short pass from fly-half Craig McMullen before producing an electrifying burst through the middle for a superb solo try which Stimpson converted to put Leicester firmly back in contention.

Rowntree joined them in the 59th minute, replacing Perry Freshwater and Leicester were suddenly firing on all cylinders.

Burke missed two penalties, which could ultimately prove costly for Harlequins and Leicester, whose pack had looked so ineffective before the introduction of their stars, suddenly provided the platform to produce a threat every time they went forward.

Burke made amends with a 71st minute penalty to increase the Harlequins' lead to 26-13 but Leicester had no intention of letting the match, and their European hopes, slip away.

Stimpson saw a penalty attempt, from long range, rebound from the post but Leicester stormed forward.

They controlled a scrum near the Leicester line superbly for Martin Corry to pick up and touch down in the 77th minute to leave Stimpson an easy conversion to reduce the arrears to six points and he cut them even further with a long-range penalty two minutes into injury time to leave Leicester as the overwhelming favourites for the second leg.