Williams did get the jump in the second set, breaking Pliskova in the fourth game. But she was broken in the fifth and seventh games in a match that seemed sure to drag on, never a pleasant prospect for a 36-year-old who struggles with Sjogren’s syndrome, an energy-sapping autoimmune disease.

Witt had made a point on Sunday of noting how important it was for Williams to keep her matches as brief as possible to preserve strength for later rounds. But living in the moment — or staying alive — defined a draining third set as the players traded breaks, Pliskova getting the early jump in the third game before Williams got even at 4-4.

After holding for 5-4, Williams had her match point when Pliskova dumped a forehand into the net at 30-all. Pliskova hit a forehand approach that Williams ran down but could only float back. Just inside the service line, Pliskova hit an audacious swinging forehand volley for a winner.

Pliskova held her serve, converted the second of two break points in the 11th game and then, serving for the match, won the first three points. The match appeared over. And then it wasn’t.

Pliskova — who won 75 percent of her first-service points in play — suddenly couldn’t land one. She double-faulted on her first match point, then watched in dismay as Williams destroyed her second serve, winning the next four points to break back.

The crowd erupted, though Pliskova was already unhappy with sporadic applause for her missed first serves.