Maria Sharapova, Agnieszka Radwanska advance at WTA Finals

Maria Sharapova finished a perfect 3-0 in round robin play to advance to the semifinals of the WTA Finals in Singapore, and her victory over Flavia Pennetta in the final match of Red group play allowed Agnieszka Radwanska to move on as well.

Radwanska entered the day 0-2, but dispatched top-ranked Simona Halep 7-6(5), 6-1 for her 500th career victory. She then need a straight sets victory from Sharapova to advance.

Pennetta had won the past three meetings with Sharapova and broke in the first game of the match. She took a 4-2 lead before Sharapova won five of the next six games to take the first set 7-5.

The third-ranked Sharapova then cruised to a 6-1 victory in the second set, ending the career of her No. 7-ranked opponent, who announced she would retire at the end of the season.

"I'm happy to have had the chance to play this tournament," Pennetta told reporters after the match. "I think to have my last match against Maria - it was amazing to play such a good champion. And it was also a good way to say goodbye, because when you lose against such a good player, there aren't too many things to say.

"Right now I feel completely normal, like it's not my last match - I don't know why. Maybe in a few days I will feel more different. But right now it's so far, so good."

Sharapova was the only player to win more than one match in the Red group, and impressive feat considering it marked her first full matches since Wimbledon.

"I've lost the last couple of times against Flavia. I know what a tough competitor and opponent she is," Sharapova said. "I just wanted to get a little bit of revenge before she goes out of the game!

"I just heard this was her last match. It's really sad to see such a great champion go. She's had an incredible career, and I was so happy she got the Grand Slam at the U.S. Open. I was smiling for her."

Sharapova will play the No. 2 qualifier from the White group on Saturday, while Radwanska will play the top advancer from the group.

The White group concludes its round robin play on Friday, with Garbine Muguruza (2-0) playing Petra Kvitova (1-1) and Angelique Kerber (1-1) playing Lucie Safarova (0-2).