World No.1 Serena Williams has stormed into the final of the WTA tournament at Stanford in which she will play Germany’s Angelique Kerber.

Serena Williams stormed into the final of the WTA hardcourt tournament at Stanford on Saturday, winning the last eight games of a 7-5, 6-0 victory over Andrea Petkovic.

The world number one and top seed, playing her first tournament since a disappointing Wimbledon campaign in which she was slowed by a virus, will face third-seeded German Angelique Kerber in Sunday’s final.

Kerber, ranked eighth in the world, saved a match point on the way to a 4-6, 7-6 (7/4), 6-2 victory over 59th-ranked American Varvara Lepchenko.

Petkovic, 26, who ousted 34 year-old Venus Williams in the quarter-finals on Friday, pushed 32 year-old Serena hard in the opening set as they battled through the first 11 games without a break of serve.

After holding for a 6-5 lead, Williams turned the tide in the 12th game, although she needed a fifth set point against Petkovic’s serve to gain the break and the set.

There was no stopping the 17-time Grand Slam champion from there. After a first set lasting 50 minutes Williams polished off the second in 27, breaking Petkovic a fourth time when the German sent a forehand long on match point.

“I’m really excited,” said Williams. “Andrea and I both had really long matches yesterday, so I was just hoping to come out again today with fresh legs and just try to do the best I could out there. My body feels great.”

Petkovic was trying to become just the eighth player to beat both Williams sisters in the same tournament, and the first since Jelena Jankovic did so at Rome in 2010.

“Playing one of them is a lot,” Petkovic said. “Playing two of them in a row was so strange, like playing a video game. It was the most awkward situation I’ve ever been in. I idolised them and admired them growing up.”

On Sunday, Williams will be seeking a fourth title of 2014. She has won all three finals she has reached this year, at Brisbane, Miami and Rome.

When the WTA world rankings are next released, she will have been number one for 200 non-consecutive weeks in her career, but Williams has struggled this year in Grand Slams, failing to make it past the fourth round in the Australian Open, French Open or Wimbledon.

Stanford and next week’s WTA event in Montreal are part of her build up to the US Open, her last chance in 2014 to add another major title to her resume.

Williams has won four of her five career meetings with Kerber, who saved a match point while trailing 4-5 in the second set against Lepchenko, who was playing in just the second WTA semi-final of her career.

“I have no idea how I did it,” Kerber said of her escape. “I was just trying to fight until the last point and believe in me, and just try to change my game in the middle of the match, but I have no idea how I won.”