Manchester United were grateful to a Zlatan Ibrahimovic hat-trick to give them a comfortable 3-0 first leg lead over St Etienne after an improved second half showing following a patchy opening 45 minutes.
United have never lost a home match against French opponents but they certainly tried to end that record with a patchy first half performance that saw them take a fortunate lead, fail to build on that and allowed a bright St Etienne outfit to cause them problems throughout.
Within the first couple of minutes slackness in the United defence through Eric Bailly allowed Romain Hamouma to run clear on goal but keeper Sergio Romero held him up well and forced the Frenchman wide.
Still the French team looked lively and it took a fortunate deflected free kick from Zlatan Ibrahimovic on 15 minutes to give the hosts the lead. The visitors will feel doubly aggrieved as the Swede won the free kick himself in soft circumstances.
Instead of calming down at the back United continued to concern their fans and Daley Blind almost gave a penalty away with a clumsy tackle. Yet the Red Devil's were also creating chances of their own.
But it was St Etienne who ended the half the stronger as Henri Soviet twice went close. Kevin Montreal-Paquet scuffed a shot wide and Houmana was again put clear through the porous home rearguard but blasted over.
United reacted first after the break and Ibrahimovic quickly had a headed goal disallowed for offside. Again Martial dribbled into the penalty area and when his shot was blocked by Ruffler, Ibrahimovic forced the keeper to palm the loose ball for a corner.
At this stage it was all the home side pressing finally waking up the Old Trafford faithful who had up to this point been out-shouted by their frenzied French counterparts.
The question was would the home side increase their lead or regret making their dominance count particularly when Paul Pogba curled narrowly wide from distance then made a hash of a far post opportunity before later heading against the cross bar from six yards.
But just as St Etienne looked to to have run out of ideas United contrived to allow substitute Nolan Roux to race through a chip the ball over Romero but on to the roof of the net. And almost immediately they paid for that miss as the Red Devil's doubled their advantage.
Ibrahimovic was in the perfects position to stab home from close range after substitute Marcus Rashford's shot had been parried into his path.
And the Swedish star was not to be denied the match ball converting the penalty after he had been fouled from behind in the penalty area and inflicted a first European defeat in ten games on the French outfit.
Man Utd: 3 (Ibrahimovic 15, 76, 88 pen)
St Etienne: 0