Both women won their first matches at the WTA Finals on Sunday, but with different routes to success. Halep was dominant; Sharapova was resilient in her match at Singapore.

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The WTA Finals, an eight-woman tournament, is under way without the world’s best player. Serena Williams, winner of the past three finals, is on hiatus until January.

Halep, the No. 1 seed in the finals, proved herself to be a leader for the championship by overwhelming U.S. Open winner Flavia Pennetta 6-0, 6-3. It was a measure of revenge for Halep, who lost to Pennetta in the Open semifinals.

The first set took all of 26 minutes. And there was no sign of problems with an ankle injury that limited Halep in recent matches.

Sharapova wasn’t as good, and her opponent was much better. She beat Agnieszka Radwanska 4-6, 6-3, 6-4. It was Sharapova’s first full match since Wimbledon, and it was clear she wasn’t at her best early on. In addition to lack of sharpness, Sharapova had to prove she was past recent leg and arm injuries.

In contrast to Halep’s rapid victory, Sharapova needed 2 hours, 48 minutes to win in the round-robin event.

“Coming into this event, I tried to do everything I could to be healthy and although I didn’t play my best tennis today, sometimes that’s not what matters,” Sharapova said.

“I’m so happy that I got through and have a chance to play two more matches to end the season and hopefully more, so I couldn’t be happier at this point.”

Ahead is a match between Halep, who many observers see as the next dominant women’s player, and Sharapova. Halep was a finalist in 2014 and beat Williams in an earlier match.

“I feel the same now as I did against Serena,” Halep said Sunday. “I can play my best tennis here yet I didn’t play my best today, but I played good tennis. I played solid and was dominating the match.

“I have confidence and I just want to stay focused, because after tomorrow I will have a tough match. I expect every match to be difficult, so I just want to stay focused and to believe that I have my chance.”

Monday’s singles matches are the first in the other half of the field. Garbine Muguruza, the tournament’s second seed, faces Lucie Safarova before Petra Kvitova plays Angelique Kerber. Kvitova is the only former WTA Finals winner in the field.