Kai Havertz came off the bench and scored a 91st-minute winner as Arsenal clinched a 1-0 victory over Sporting in the first leg of their Champions League quarter-final in Lisbon.
Just as it seemed a cagey game was heading for a stalemate, Havertz produced a brilliantly composed finish from fellow substitute Gabriel Martinelli's pass to give the Gunners a potentially crucial advantage ahead of next week's second leg.
Arsenal were indebted to David Raya for keeping the scores level before that, with the goalkeeper having superbly tipped a Maxi Araujo shot onto the crossbar early in the game before making vital saves from Geny Catamo and Luis Suarez late on.
Arsenal had a Martin Zubimendi goal ruled out by VAR for an offside against Viktor Gyokeres but otherwise struggled to create chances in a European away performance focused on limiting the opportunities of their opponent, at least until Havertz's late heroics.
The result ensures a positive response to their consecutive cup losses to Manchester City and Southampton and puts Arsenal on course to reach back-to-back Champions League semi-finals for the first time in the club's history.