WIMBLEDON, England (AP) Defending champion Serena Williams has defeated unseeded Petra Kvitova in straight sets to reach her third straight Wimbledon final and sixth overall.

The top-ranked Williams overcame a stiff challenge in the first set from the 62nd-ranked Czech player, then pulled away for a 7-6 (5), 6-2 victory on Thursday.

Williams is now one win away from her fourth Wimbledon title and 13th Grand Slam championship.

She advanced to Saturday's final against 21st-seeded Russian Vera Zvonareva, who rallied to beat Tsvetana Pironkova 3-6, 6-3, 6-2 in the day's first match on Centre Court.

It's the 10th time in the last 11 years that at least one of the Williams sisters has advanced to the final. Venus and Serena have won eight titles.

Zvonareva reached her first Grand Slam final. The 21st-seeded Russian came from a set down to beat the 82nd-ranked Bulgarian 3-6, 6-3, 6-2 in the day's first semifinal on Centre Court. She was in complete command after breaking in the sixth game of the second set, winning 10 of the last 13 games.

Zvonareva has battled a reputation for fading in big matches but held her nerve on the biggest stage in tennis.