Marseille's decision to field third-choice goalkeeper Elinton Andrade backfired as his mistake gifted Bayern Munich the opening goal in their Champions League quarter-final tonight.
The 32-year-old, preferred to number two Gennaro Bracigliano with first choice Steve Mandanda suspended, allowed Mario Gomez's shot to squirm under his body in the 44th minute of the first leg at the Stade Velodrome.
It was Gomez's 11th Champions League goal this season, behind only Lionel Messi, and 37th in all competitions and kept them on course to reach the final at their own Allianz Arena stadium.
Arjen Robben added a classy second midway through the second half to put the Germans on the brink of a place in the last four.
It was hardly a vintage Bayern display, but it did not need to be to beat a Marseille side in the midst of an awful run domestically. Saturday's draw with Nice ended a run of seven straight defeats in all competitions, including a cup defeat to lowly Quevilly.
Marseille should have gone in front in the seventh minute when Manuel Neuer produced a brilliant one-handed save diving to his left to keep out Rod Fanni's powerful header from a Mathieu Valbuena corner.
The rebound fell to Loic Remy, who could only slice his effort into the side-netting when it looked easier to score.
The hosts were looking vulnerable at the back, though. Thomas Muller hesitated when he got beyond the last defender, eventually choosing to pull the ball back from the byline when an early shot would have been the better option and his pass evaded everyone in the area.
Neither side were giving likely semi-final opponents Real Madrid any cause for concern, with both squandering possession far too easily.
But Neuer had to be alert against to save from Remy at his near post after the striker had pounced on a poor clearance.
Bayern struggled to seriously test stand-in keeper Andrade until a minute before half-time his mistake handed them the lead.
With Marseille appealing in vain for a free-kick for handball at the other end, a Bayern counter-attack ended with Arjen Robben playing in Gomez. The Germany striker's side-foot shot from the edge of the area was hardly unstoppable or perfectly placed, but still squirmed under Andrade's body and into the net.
The visitors had another opening early in the second half, but Fanni got back to clear the ball off the toes of Muller as he bore down on goal.
Neuer then comfortably held a header from Andre Ayew.
Andrade went a little way to making up for his earlier error by blocking another Gomez shot from inside the area before Remy almost embarrassed Jerome Boateng.
The Marseille man won the ball off the defender on the edge of the area, but his stabbed shot hit Neuer and deflected away.
But Bayern doubled their lead in the 69th minute and, if their first goal was fortunate, this one was beautifully crafted and expertly finished.
Robben played a neat one-two with Muller, breaking into the area from the right as he ran on to the return pass and then sliding a finish into the far corner.
That goal appeared to break the hosts' resolve and they did not look like getting one back to give them hope for the second leg as Bayern saw out a comfortable win.