WIMBLEDON, England (AP) Serena Williams was pushed to three sets on Centre Court before beating fellow American Alison Riske 6-4, 4-6, 6-3 to reach her 12th Wimbledon semifinal.

Williams broke for a 5-3 lead in the third set when Riske double-faulted on the fourth break point of the game, and then served out the win with an ace.

Williams was down a break twice in the opening set but came back both times and broke again in the final game. But in the second set, Riske broke for a 5-4 lead before holding serve to even the match.

Riske converted all five break points she created, while Williams needed 16 opportunities to break six times.

Williams is seeking an eighth Wimbledon title and 24th Grand Slam victory, while Riske was playing her first quarterfinal at a major tournament.

Williams was due back on Centre Court later Tuesday to play mixed doubles with Andy Murray.