Serena Williams downs Agnieszka Radwanska, books Toronto final with Sorana Cirstea

World number one Serena Williams defeated Agnieszka Radwanska 7-6 (7/3), 6-4 on Saturday to reach the final of the WTA Toronto tournament, where she'll face Sorana Cirstea.

Williams maintained her perfect record over Radwanska.

The American has beaten the world number four from Poland six times, a run that included a triumph in the 2012 Wimbledon final and, most recently, in the semi-finals at Miami this year.

Williams next faces unseeded Romanian Cirstea, who toppled fourth-seeded Li Na of China 6-1, 7-6 (7/5).

The victory over 2011 French Open champion Li continued a dream run for 27th-ranked Cirstea in the $2.4 million hardcourt tournament.

She also beat former world number ones Caroline Wozniacki and Jelena Jankovic, as well as defending champion Petra Kvitova, en route to the final.

A tight first set saw Williams and Radwanska trade four service breaks, the American holding serve to force the tiebreaker.

Williams took control early in the tiebreaker, taking a 3-1 lead, and gave herself a triple set point with a cross-court winner for 6-3.

She needed just one of those set points, firing an ace to seal the set.

Williams went down a break to trail 3-1 in the second, finally regaining the break to level the set at 3-3 with a fierce overhead winner to end a long rally on her third break chance.

She saved a break point to hold for a 5-4 lead, and broke Radwanska in the last game with a backhand winner followed by a high forehand volley on match point to seal the victory in one hour and 51 minutes.

Cirstea was looking forward to her shot at Williams.

"I am really excited for what's happened this week and for tomorrow," she said. "Everything now is coming together for me."

The 23-year-old Cirstea cruised through the first set before Li jumped out to a 4-1 lead in the second.

Cirstea won five of the next seven games. She was unable to convert two match points in the 12th game as Li forced the tiebreaker.

In the decider, Li again gained the advantage, but Cirstea won six of the last seven points and clinched the semi-final victory on her third match point when a mistake-prone Li double-faulted.

"I'm happy with how I fought in the end and I'm really happy to finish the match in two sets," said Cirstea, who won her lone singles title five years ago at Tashkent.

Cirstea blasted 17 winners and converted four of seven break points in the 87-minute match, and was pleased that she was able to overcome some nerves and thwart Li's second-set rally.

"At 4-1 I was getting quite tight," Cirstea said. "I just tried to focus on every point and not think about the score."

Li, who usually plays best when coming from behind, never got her serve untracked Saturday. She saved two match points in the 11th game of the second set but was hurt by half a dozen double faults.

Li, playing her first tournament since a quarter-final exit at Wimbledon, said she will just have to regroup for the next tournament.

"When I lose a match I am always a little bit sad," Li said. "But still have to find some positives.