Braam van Straaten's conversion of a Diego Albanese try in the fifth minute of stoppage time, meant heartbreak on the road once again for NEC Harlequins, who deserved more than a single bonus point from their evening's work.
Quins had fallen 13-3 behind midway through the first half thanks to two penalties from the Sale Sharks bound van Straaten, who also converted a well-worked try from Chris Hall, after some delightful handling by Dan Hyde and Alan Dickens along the left flank.
However, a second penalty from Paul Burke in first half injury time, proved to be the catalyst that Quins needed to come roaring right back into the match after the break, and to lead 19-13 and then 22-16 with 15 minutes to go.
Burke's conversion of a sparkling individual score from 42 metres out by Dan Luger levelled the scores early in the second period, before two further Burke penalties, after van Straaten had missed a long range effort, saw Quins dreaming of a second successive away win.
Van Straaten reduced the deficit on the hour, only to see Burke kick the visitors back in front by six points five minutes later, with a 25 metre drop goal.
Quins pressed for what would have been a decisive score, but Leeds came back in the dying minutes and set-up plenty of set-piece ball deep inside the visitors twenty-two. With the Quins defence looking rock solid, they had appeared to have done enough to claim the spoils, especially when Will Greenwood forced Canadian international winger Winston Stanley into touch a few metres from the line.
However, referee Chris White had judged that Quins were offside from a goal-line blitz defence, and not only awarded the home side a penalty but sin-binned Luger.
It proved a crucial decision because with Quins a man down, Leeds took a tapped penalty and spread the play out to the right where Albanese was able to take advantage of the extra man to run in and give van Straaten the chance to win the game, which he gratefully accepted.
During week commencing 22nd April Harlequins will launch an innovative, new Membership Scheme which will replace the existing Season Ticket Holder Programme. Further details of the scheme will be announced in due course.