Eduardo da Silva capped an Arsenal comeback from an early two-goal deficit to score the decider in a 3-2 victory over Standard Liege in the opening Group H game of the Champions League.
Eduardo, who only started after UEFA overturned his two-match ban for diving earlier this week, slotted the winner in the 81st minute from close range.
Arsenal’s third-string goalkeeper, Vito Mannone, had a nightmare start when Eliaquim Mangala scored in the second minute and Milan Jovanovic wrongfooted him to convert a penalty two minutes later.
Arsenal’s Nicklas Bendtner slotted home from a tight angle on halftime.
Thomas Vermaelen scored in a goalmouth scramble in the 79th before Eduardo gave the Gunners victory two minutes later.
In the other group game, Olympiakos beat AZ Alkmaar 1-0.
Standard’s stunning start punished its Premier League opponents for careless and nonchalant play.
Eduardo was supposed to produce goals for Arsenal but his bad early clearance gave Mangala the chance to put Standard ahead with a left-footed drive that surprised Mannone.
Immediately after the kickoff to resume play, Arsenal again clumsily lost the ball and Jovanovic took the defense by surprise until he was brought down William Gallas just inside the box.
If Standard had to start its campaign without captain Steven Defour, who broke his foot over the weekend, Arsenal had a half dozen on leave because of injury or illness, including goalkeeper Manuel Almunia, forwards Robin van Persie and midfielder Denilson.
Still, Arsenal is a near perennial Champions League contender and a semifinalist last season, and still had the whole of the second half to pull the game its way. Standard started looking for the counterattack and when Jovanovic was out injured in the 59th minute, the situation of the underdog became dire.
Arsenal dominated and the weight of its close skills started to pay off, wearing down the Standard players.
After the scrappy goal by Vermaelen, which Standard complained about because Alexandre Song appeared to handle the ball, Arsenal sensed victory was still possible.
Eduardo had been listless most of the match, but suddenly came alive. He forced Sinon Bolat in a sterling save one minute after the equaliser, but was in the right place on a corner to tap home the winner with his knee.
