A dramatic late header from the Ghanaian has given OM the vital edge heading to the second leg in Milan, which takes place in three weeks
It was the home side that dominated proceedings against the defensively-minded Serie A outfit, but they lacked the offensive nous to really worry the out-of-form visitors until stoppage time, when Andre Ayew headed the winning goal.
OM probed in the first half, enjoying plenty of possession but lacking real penetration with their attacking movements, while Inter’s response typically came on the counterattack, carving out several openings.
The best of these came early to Diego Forlan, who could not generate sufficient power from Esteban Cambiasso’s cross to steer the ball beyond Steve Mandanda, who, nevertheless, had to react well to turn the Uruguayan’s shot over.
Cambiasso would be the chief threat to OM in the first period down the left hand side, instigating several of his side’s best moves. Ten minutes before the break he beat the offside trap and cut a pass back to Mauro Zarate, but from a very good position the striker could only tamely sidefoot at goal, allowing Mandanda to get down easily to save.
Just before the interval, the Argentine had a chance to go it alone, but his shot had the sting taken out of it by Souleymane Diawara’s block.
Marseille were not anonymous, however. After only three minutes Benoit Cheyrou had a shot from range deflected narrowly wide after he was given too much room outside the box, while Cesar Azpilicueta had a vicious strike dip over the top.
Perhaps OM’s best chance came from a Mathieu Valbuena free kick that would surely have been converted had Brandao and Souleymane Diawara not got in each other's way.
The second period followed much the same pattern of the first, though Inter’s insistence on defending ensured there would be fewer opportunities for either side.
Brandao did have one tame header saved by Julio Cesar and Jeremy Morel slashed a powerful shot comfortably wide.
Inter offered even less of a threat. It took them nearly half an hour to muster a meaningful shot on goal, with Dejan Stankovic unable to react quickly enough from eight yards to seriously worry Mandanda following Wesley Sneijder’s free kick.
Late in the game, Andre Ayew had a trio of headed efforts at goal following Morgan Amalfitano crosses, but the decisive moment came after his own late shot had been saved. From the resultant corner, the Ghanaian glanced the winning goal, having escaped the marking of Cristian Chivu.
Given the paucity of chances in the match, a scoreless draw might have been apt, but the late strike from the hosts has potentially plunged a dagger into the heart of Claudio Ranieri's spell as Inter coach, following the Nerazzurri's six defeat in seven games.