Florian Thauvin put Marseille within touching distance of a place in the UEFA Europa League final with a controversial opener as his side beat Red Bull Salzburg 2-0 at the Stade Velodrome.
Thauvin headed home in the 15th minute from a pinpoint Dimitri Payet free kick, although subsequent replays suggested the ball had also touched his hand on its way into the net.
Substitute Clinton Njie put the Ligue 1 side in a commanding position heading into next week's second leg in Austria when he scored their second goal three minutes after coming off the bench.
Marseille had made an impressive start against their opponents with Kostas Mitroglou bringing a good save out of Salzburg's Alexander Walke with just four minutes on the clock.
Jordan Amavi was causing all sorts of problems for the visitors down the right flank and it was no surprise when the irrepressible Payet paved the way for his side to grab the early advantage.
Morgan Sanson struck another chance wide from long range before Salzburg belatedly stirred, with Duje Caleta-Car heading a good chance over the bar from a corner.
The lively Mitroglou had a shot blocked in the box before the visitors missed the chance to move level just before half-time when full-back Andreas Ulmer blazed his shot high.
The visitors felt they were the victims of more injustice eight minutes into the second half when they had strong penalty shouts waved away after Stefan Lainer fell under the challenge of Maxime Lopez in the box.
Hannes Wolf had Salzburg's best chance one minute later when he burst into the box only to see his rising shot brilliantly tipped one-handed over the bar by home keeper Yohann Pele.
Njie's introduction on the hour mark would make a big difference, as the striker fired home with one of his first touches after Payet cleverly cut the ball back in the box.
Increasingly desperate, Salzburg missed half-chances from Valon Berisha and Munas Dabbur, and their disappointing night was sealed when substitute Fredrick Gulbrandsen hit the woodwork in the dying minutes.