Jesse Rodriguez scored the only goal of the match from a run that could/should have been spotted and stopped.
He's at Stoke City on loan from PSG following the record signing of Neymar Jnr from Barcelona for a ridiculous world-record fee of $263 million.
Alexandre Lacazette had a goal ruled out as offside in a controversial decision by the match officials.
"We have 33 players at the moment and that's too many. I'm not thinking about buying players tonight," said Arsene Wenger after the game."This remark will most likely ignite the fury of the fans who are still looking for quite a few signings before the transfer window closes on 30th August though there've been speculations the transfer window might be pushed back.
"I think we scored a goal that is not offside," Wenger added in his postmatch interview.Manchester United thrash Swansea City 0-4
"It is a very easy decision. When the ball is kicked he is not offside, Lacazette."
"It was a very frustrating evening. I feel we had plenty of chances to score and didn't."
"We know in this kind of game it is important not to make a mistake but straight after half-time we were too sluggish on defending and we paid for it."
"After that we did not move the ball quickly enough and we did not combine well. I believe some teams will get something here, that is why if you want to play at the top you have to consider it three points dropped."
"We were unlucky. I think we scored a regular goal that was given offside and it wasn't offside.Goal keeper Jack Butland showed some class in performance yet again.
"It is a difficult defeat to swallow. We had chances - we should have won the game comfortably. You don't want to lose games that you should win."
"It was frustrating getting caught cold for the goal. Defensively there is no excuse. We gave them a cheap goal. I was not convinced by our central defence."
Arsenal are currently 11th and Stoke City 13th in the table.