Serena Williams will be aiming for her eighth title of the season after advancing to the Rogers Cup final with a tough 7-6 (3), 6-4 win over Poland's Agnieszka Radwanska on Saturday.

Williams, a two-time Rogers Cup champion, will face Romania's Sorana Cirstea, a 6-1, 7-6 (5) winner over Li Na of China in the other semifinal.

Williams is now 6-0 against Radwanska, including the Wimbledon final last year.

"It was definitely one of the tougher matches," she said. "Obviously, Wimbledon was another tough one. We actually have a lot of good matches."

Williams will be trying to match her career high for titles in a single season with eight, which she last accomplished in 2002. She has 53 titles overall in her career, tied for ninth place on the all-time WTA title list with Monica Seles.

Williams has beaten Cirstea in their two previous matches. The 27th-ranked Romanian won her lone WTA Tour in 2008 at Tashkent.

Radwanska and Williams traded breaks twice in the first set, with the Pole keeping up with Williams' imposing power game. In the tiebreaker, Williams blasted a cross-court winner for a 6-3 advantage and then hit an ace on set point.

Williams called for a medical timeout early in the second set because of what she later said was an upset stomach. She looked slightly out of sorts early in the set, going down a break and screaming at the ground after blowing an easy overhead smash.

But she broke back and took a 4-3 lead by running Radwanska around the court with blistering groundstrokes. She won a nearly 10-minute game to pull ahead 5-4 and broke Radwanska to finish off the match in 1 hour, 52 minutes.

"That's what makes her No. 1 in the world, playing unbelievable in the very important moments, and just hitting some very powerful shots," Radwanska said. "I couldn't really do anything about that out there tonight."

Cirstea ousted two former world No. 1s in Jelena Jankovic and Caroline Wozniacki this week and beat sixth-seeded Petra Kvitova in the quarterfinals.

"It doesn't matter who I beat the day before or what I've done," she said. "It's just another day where I have to get out there and do the things to show the work that I've put in."