Play resumed once Palace's goalkeeper limped down the tunnel, and United began working the ball down Garnacho's side with more purpose than they'd shown in the first ten minutes.
Garnacho drove inside off his fullback and forced a scrambled corner that Palace cleared under pressure.
Two minutes later, Mount received on the half-turn just outside the box and slipped a pass wide for an overlapping run that never quite arrived in time.
Dalot got forward on the next attack and won the ball back into the corner, cut it into the six-yard box, but a Palace defender read the cutback and hacked it clear before Martial could get a touch.
The goal United had been building toward finally arrived in the twenty-first minute.
The move began with Casemiro switching play from left to right in one motion, Palace's shape shifting a half-second too late to compress the space, and United worked the ball back into the same wide channel that had produced two warnings already.
