Singapore, Oct 26 (IANS/EFE): Romania's Simona Halep and Russia's Maria Sharapova won their matches in the first round of play at the WTA Finals in Singapore.

Halep got revenge against Italy's Flavia Pennetta, who beat her in the US Open semi-finals, rolling to a 6-0, 6-3 win in 70 minutes on Sunday.

Pennetta had dominated the Romanian 6-1, 6-3 in their semi-final match on September 11 at Flushing Meadows, where the Italian won her first Grand Slam title a day later.

Sharapova, for her part, overcame 12 double-faults to beat Poland's Agnieszka Radwanska 4-6, 6-3, 6-4.

The Russian, who had played just one match since Wimbledon due to a shoulder injury and appeared rusty at times, will take on Halep next in Red group competition in the eight-player, season-ending tournament's next round-robin matches.

The Red group is made up of Sharapova, Halep, Radwanska and Pennetta, who announced after winning the US Open that she would retire at the end of the season.

Spain's Garbiñe Muguruza, the finalist at Wimbledon, will make her debut on Monday in White group action.

The Spaniard has been drawn in the White group along with Czech Petra Kvitova, Germany's Angelique Kerber and Czech Lucie Safarova.

Muguruza will play Safarova, the French Open finalist, who beat the rising Spanish star in the quarter-finals at Roland Garros in their only career meeting.

The Muguruza-Safarova match will be followed by the match pitting Kvitova against Kerber.

Kvitova, a two-time Wimbledon champion, has a 4-2 record against Kerber, winning their last three meetings.

American world No. 1 Serena Williams, who won the other three majors of the season and came within two matches of pulling off a rare calendar-year Grand Slam, announced earlier this month that she would not play the WTA Finals because she needed to give her body a chance to recover from the gruelling season.