Serena Williams of the US serves to Agnieszka Radwanska of Poland during their women's semi-final tennis match of the Rogers Cup tennis tournament in Toronto, August 10, 2013. The image is an in-camera, multiple exposure photograph. [Photo/Agencies]

TORONTO, August - World No 1 Serena Williams continued her success at the Rogers Cup with a tough 7-6 (3), 6-4 victory over No 4 Agnieszka Radwanska in the semi-final round on Saturday in the Canadian city of Toronto.

Williams, winner of 16 Grand Slam singles titles, will be looking to add to her resume. In her path to the final victory is No 27 ranked Sorana Cirstea of Romania, who stunned China's French Open winner Li Na in straight sets in the earlier semi-final match.

Williams and Radwanska battled in a closely-contested match that entertained the Toronto crowd. Williams used her power to counter the long rallies of the trickier Radwanska. In the end, the American's power was just too much for the Pole to handle.

"It was definitely one of the tougher matches," said Williams after the game. "I let her play her game, which is what she wanted to do, but I wasn't able to play my game as much."

Despite dictating the style of the match, the 24-year-old Radwanska still found herself chasing down deep ball after deep ball and exerting the most energy between the two players. Near the end of the first set, the Pole believed Williams stepped up her game to the next level.

"She really start to play much better in the end of the set, especially in the second set, and playing very aggressive and very deep balls," said Radwanska. "This (is) what makes her No 1 in the world, playing unbelievable in very important moments...I couldn't do anything, you know, about that."

In the other match, world No 5 Li Na was upset by Sorana Cirstea of Romania in straight sets, 6-1 7-6 (5).

The 23-year-old Romanian made quick work of Li in the first set in only 21 minutes.

In the second set, she overcame a 4-1 deficit to advance to her third career WTA final and first in nearly five years. She won the Tashkent Open in Uzbekistan when she defeated German Sabine Lisicki in October 2008.

Regardless of a win or loss, the Romania is thankful to still be in the tournament. During her second round match against world No 10 ranked Caroline Wozniacki, she fought off two match points to force a third set which she won.

"Look at this. I could have been out in the second round or in Cincinnati getting ready for my first round, and here I am playing final, you know," said Cirstea. "So it's the difference between making it and not making it. It's very, very small. That's why now I'm trying to focus on each point, each match, and just try to be in the moment because that's what matters the most."

Not knowing who she would be facing, Cirstea had a positive mentality following her victory over Li.

"The main thing is I still have to stay serving well, being aggressive, trying to be in control, going in the court with good mentality," said Cirstea. "I mean, no matter who is on the other side, I still have to do the same things on my side."

Williams is intrigued by the matchup against Cirstea. Despite the low ranking of her opponent, she does not see it as an easy victory.

"Last few months she has been really consistent," said Williams. "She is just a player who has finally found herself, and she's playing better and better and getting more confident. It's going to be a really tough match."

As two-time winner of the Rogers Cup tournament, a victory in the finals tomorrow will bring her one step closer to tying Monica Seles' record of four Rogers Cup titles.