Serena Williams roared back after falling behind in the third set to beat Ana Ivanovic and reach the semifinals of the Bank of the West Classic. Photo by: Jeff Chiu/AP

Stanford, California – Serena Williams roared back after falling behind in the third set to beat Ana Ivanovic 2-6, 6-3, 7-5 on Friday and reach the semifinals of the Bank of the West Classic.

It will not be an all-Williams match-up however, as elder sister Venus was beaten 6-1, 3-6, 7-5 by Andrea Petkovic.

It was far easier going in the quarterfinals on the other side of the draw, with Varvara Lepchenko dropping only one game against qualifier Sachia Vickery and her semifinal opponent Angelique Kerber losing only three against Garbine Muguruza.

The top-seeded and top-ranked Serena Williams dropped three consecutive games to fall behind 4-3 and then ripped seven straight points in front of a sellout crowd at Stanford.

“I can play loads better and that's good that I believe that,” Williams said. “I thought we both played very well.”

“She's not easy to play. She always gives 100 percent. I just kept fighting, stayed calm and focused on what I wanted to do.”

Williams is assured of a 200th non-consecutive week at the top of the ladder while Ivanovic will return to the top 10 for first time in over five years.

“It feels great to be back in the top 10,” Ivanovic said. “I've worked so hard to get back. I've set high goals for myself and this was the first one.”

Ivanovic took an injury timeout down 5-2 in the second set. She pinched a nerve in her left side when she came down after a winning shot.

“It made it hard to move to the right but she was playing well at that time and using the angles,” Ivanovic said. “Playing the No.1 player in the world that close and having opportunities was encouraging.”

Petkovic will face Williams in a semifinal between two players who have had to deal with more than their fair share of serious injury setbacks in recent years.

Following a shaky start, the 25th-ranked Williams picked up her game in the second set and appeared poised to take over the match, but the German found an extra gear in the third.

“I was not as on as I was on previous days,” Williams said. “I had to fight through that and I almost did that. But she played the last two points better.”

Petkovic has already won two titles this season and reached the semifinals at the French Open.

“I played one of my best games in the third set at 5-5,” Petkovic said. “Before that it was a weird match. There were so many momentum changes and so many ups and downs, I felt like I played four different matches in one.”

Lepchenko took care of Vickery, 6-1, 6-0, to earn her 400th career win, which includes all levels.

“It was hard to play someone from the United States who I know very well,” Lepchenko said. “I've practiced with her often before. I knew this match would be mentally tough but was just trying to play the best tennis I could.”

She will meet third-seeded Kerber, who topped Muguruza, 6-2, 6-1.

“She is definitely one of the tougher lefty opponents out there, so I will have to play and fight for every single point,” Lepchenko said. “I'm going to stay focused on my game and hopefully things will work out well for me.” – Sapa-AP