The Gunners dominated for 90 minutes, but couldn't find a way past Milan's Aussie keeper Zeljko Kalac until the final minutes when a mazy run from substitute Theo Walcott led to his cross taking out the visiting keeper and leaving Adebayor with an empty net to nod home. But the Togo striker's effort amazingly cannoned off the crossbar and with it Arsenal's last chance to edge this first-leg.
Arsene Wenger's side took the game to the reigning European champions from the off, but despite the best efforts of Cesc Fabregas and company, Milan's defence stuck to their task to leave the tie evenly balanced ahead of the return leg at the San Siro in a fortnight's time.
In the first-half, Eduardo slipped as Bacary Sagna sent a dangerous cross across goal, while Senderos just failed to connect with a Cesc Fabregas corner.
The Gunners finished the half strongly and created the best opening of the first 45 minutes when Emmanuel Eboue tied Paolo Maldini in knots, before teeing up Mathieu Flamini, but his shot was comfortably saved by Kalac.
Arsenal made a bright start to the second period when Fabregas' corner caused confusion in the area and it struck Kaka's chest before bouncing just wide of goal.
Alexander Hleb's fantastic run down the right then carved Milan wide open but Eboue's 20-yard shot missed the target by inches. Eduardo then fired a shot on the stretch just over the bar as the hosts upped the tempo, before Adebayor had the ball in the net - only to see his effort correctly flagged offside after he stabbed past Kalac.
Fabregas then tried his luck from 25 yards after some space opened up in front of him, but his low drive was again too easy for Kalac.
Then came Wenger's rash of substitutes and Adebayor's amazing last-gasp miss.