London Welsh looked to have secured a losing point following a magnificent second-half comeback in their 29-19 Aviva premiership defeat against London Wasps at Adams Park, Wycombe.
But the Oxford-based Welsh were denied by a late penalty from Lee Thomas in the first league meeting between these two famous clubs.
It was Wasps who claimed the extra point, for scoring four tries – two each from wingers Christian Wade and Tom Varndell – in a match in which Wasps never fell behind.
However, second-half tries from Phil Mackenzie and Franck Montanella kept the Exiles in contention.
It was the first competitive meeting between the two sides since a John Player Cup tie in March 1979, which was won by Wasps. Both sides were forced into late changes ahead of kick-off.
James Haskell missed out through illness for Wasps, with his place at openside flanker being taken by Jonathan Poff. Meanwhile, Exiles No 8 Ed Jackson failed a late fitness test and was replaced by Alfie To'oala.
Wasps opened the scoring in the third minute when full-back and captain Hugo Southwell fed winger Wade, who crossed over in the corner.
Wasps’ Nick Robinson and Welsh's Gavin Henson traded penalties before Wasps extended their lead whenVarndell finished off a flowing move started on halfway. The first half was largely a scrappy affair, but Wasps went in 16-6 ahead after centre Lee Thomas sent over a drop-goal on the stroke of half time.
After the break, Wasps pulled further ahead when another slick move saw Robinson feed Wade again, and the 21-year-old sped away from the Welsh defence to touch down in the corner.
Welsh winger Mackenzie reduced the arrears when prop Paulica Ion set up the Canada international following a move which was started by the backs. Varndell then bagged his second, and his sixth of the season, after good work from Robinson.
Welsh hit back when Montanella was propelled over from a five-metre catch and drive. Gordon Ross's penalty three minutes from time looked to have salvaged a point for the Exiles, but Thomas’s converted a penalty in the dying moments to take it away.
It guaranteed a fourth consecutive victory for Wasps and moves them up to seventh. However, the hosts lost Joe Simpson to injury when the scrum-half was taken off on a stretcher at half-time.
London Wasps: Southwell (capt), Varndell, Masi (Daly 70), Joe Thomas, Wade, Robinson, Simpson (Danies HT) Payne, Lindsay (Rhys Thomas 57), Taulafo (Staibano 52), Launchbury, Wentzel, Johnson, Poff, Vunipola (Jones 57).
London Welsh: Voyce, MacKenzie, Parker, Jewell (Ross 73), Scott; Henson, Keats; Montanella (Bristow 77), Briggs (Bateman 80), Ion, Purdy, Corker, Mills (capt), Hills, To’oala (Denbee 62).
Referee: N Owens (RFU).