In perhaps the biggest upset of this wackiest of Wimbledons, Sabine Lisicki beat world No. 1 Serena Williams in the fourth round, 6-2, 1-6, 6-4.

Coming into this match, Williams had won her last 34 and promised to be the one to restore order to an upset-riddled draw. But with her huge serve and booming groundstrokes, Lisicki plays her best at Wimbledon and was on a streak of her own: In her last three Wimbledon appearances, Lisicki had beaten the reigning French Open champion. Nothing was more indicative of a potentially torrid day for the defending champion than the fourth deuce on Lisicki’s serve at 2-2 in the first set. Williams stepped inside the court to run the German from side to side, watching a defensive lob fall in front of her with oceans of time to think about where to put it. She put it in the net.

Struggling to capitalize on Lisicki’s second serve and missing consistently with her backhand down the line, Williams missed a sitter on that side to be broken for 2-4, then opened a disastrous service game at 2-5 with her third double fault of the tournament. She lost the must-hold game at love.

Lisicki, whose exuberant tennis is either sublime or ridiculous and never much of anything in between, capped her first game of the second set with a fantastic angled winner and her third second-serve ace, but a slight loss of intensity and accuracy on her part, coupled with a magnificent recovery of poise and accuracy from Williams saw her rapidly broken. She lost not just the second set—in which Williams made not one unforced error—but a run of nine straight games that took the American to a 3-0 lead in the third.

If this fortnight has taught us anything, however, it’s that nobody is safe from a determined underdog—or from their own mental waverings. At 3-1, 15-0, Williams experimented with a drop shot and was left applauding her opponent as Lisicki chased it down for a winner. She missed a second attempt for deuce, then missed consecutive backhands—a shot she appeared to have well under control—to be broken. Williams’ attacking returns were still working well enough to take another service-break lead, but dogged defence and the return of Lisicki’s booming groundstrokes saw the German get back on level terms again. After Lisicki read Williams’ short ball and cracked it up the line, leaving the defending champion diving desperately and taking an undignified tumble, she saved break points in her next service game with huge winners and held for 4-4 with great serving.

Williams needed a quick hold to depress Lisicki’s pretensions. Instead, at 30-30, on top of the point, her approach gave Lisicki ample time to force a volley error, and she was then pushed remorselessly onto the back foot as she was in the first set for break point. Williams saved that with a big serve, but lost her footing twice in the next point, somehow getting Lisicki’s drop shot back but unable to prevent her putting it calmly past her down the center of the court. A scrambling defensive lob from Lisicki should have been easy fodder for Williams’ smash; instead she leapt and pushed it long, another bewildering error.

Serving for the match, Lisicki displayed the best and worst of her performance today, putting an easy forehand long on her first match point and double-faulting—before producing her tenth ace and coming out on top of a long and ferocious groundstroke exchange to slam a short ball in the corner for the biggest win of her career. A few weeks ago after losing in Edgbaston, Lisicki was asked if she could beat Williams. “If I play well, serve well, I think anything is possible,” Lisicki answered. “You’ve got to believe in it.” No truer words have been spoken.

IBM Stat of the Match:Williams actually won three more points than Lisicki—99 to 96—but the German won the most important exchanges late in the match.

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