Granit Xhaka scored with a swerving long-range strike in the first half and Pierre-Emerick Aubameyang doubled the lead from the penalty spot in the 69th minute at the Emirates. The win puts Arsenal back into fourth place, two points ahead of United, and handed Solskjaer his first league loss since taking over as United manager in December. The Norwegian had 10 wins and two draws in his first 12 games.
Arsenal is now just one point behind north London rival Tottenham, with United fifth and Chelsea sixth, in an increasingly tight fight for the Champions League spots.
They had already created a number of half-chances when Xhaka gave his team the lead in the 12th minute with a shot that seemed to catch goalkeeper David De Gea by surprise, totally wrongfooting the Spaniard as it dipped into the far corner from 20 yards (meters) out.
Despite United enjoying a period of sustained pressure after the break, Lacazette was bundled over in the penalty area by midfielder Fred, and Aubameyang calmly converted from the spot in the 69th.
Aubameyang had missed a late penalty in last weekend’s 1-1 draw at Tottenham but sent De Gea the wrong way again to score his 17th league goal of the season.
Marcus Rashford had one final chance to pull a goal back for United in injury time, but headed straight at Leno.