SINGAPORE - Romania's Simona Halep kicked off her campaign for a maiden WTA Finals title in emphatic fashion with a thumping 6-0, 6-3 victory over U.S. Open champion Flavia Pennetta in the first match of the eight-woman season-ending tournament on Sunday.

While the opener proved to be a sprint, the second 'Red Group' tie was a marathon when Maria Sharapova beat Agnieszka Radwanska 4-6, 6-3, 6-4 in a full-blooded encounter marked by several swings in momentum as both players struggled on serve.

World number two Halep is the highest ranked player in the field after Serena Williams, who has won the tournament for the last three years, withdrew citing the need to rest after a year spent carrying injuries in her quest for a calendar Grand Slam.

Halep crushed Williams in round robin play a year ago before losing to the American in the final and her love of the Singapore Indoor Stadium hard court was evident in a first set she wrapped up in 26 minutes after breaking serve three times.

"I feel the same now as I did against Serena," Halep told reporters of the win. "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," she added.

The Romanian had arrived in Singapore under an injury cloud after picking up an ankle knock at the start of October, but the 24-year-old moved effortlessly around the court on Sunday and withstood Pennetta's attempts to get back into the contest.

The 33-year-old Italian played more like she had on her way to a stunning victory in New York last month in the second set but her resistance ended in a marathon eighth game when she dropped serve to trail 5-3 after staving off three break points. Pennetta, who announced she would retire from tennis at the end of the season, forced only two break points, both in the opening game of the second set, during the entire match and her unforced error count of 27 made life much easier for Halep.

Sidelined by leg and arm injuries, Sharapova had yet to complete a match since Wimbledon but after shaking off some initial rust, the Russian was back to her very best against Radwanska, playing each point as if her life depended on it. A single break was enough to give the Pole an edge in the opener but her excellent retrieving skills could do little to prevent the world number three from rallying for victory once the Russian had raised her intensity levels through the roof.

Cilic retains Kremlin Cup: Defending champion and top seed Marin Cilic retained his Kremlin Cup title on Sunday in Moscow with a straight-sets win over second seeded Spaniard Roberto Bautista Agut in a repeat of last year's final. At the combined ATP and WTA event the 27-year-old Croat fired nine aces to win 6-4, 6-4 in one hour 28 minutes to chalk up his second win over Bautista Agut in as many meetings and to grab his season's first and 14th career title. "It was a tough match," Cilic said. "This tournament becomes more and more special for me. "Coming back for second year in a row to win it again it gives my a huge satisfaction and great pleasure."

In the WTA section Russia's Svetlana Kuznetsova ended her 14-month title drought with a straight sets win 6-2, 6-1 over compatriot Anastasia Pavlyuchenkova, last year's champion, in the Kremlin Cup final on Saturday

Ferrer lifts year-end hopes with Vienna title: David Ferrer strengthened his hand in the race to the ATP season finals as the veteran Spaniard won the Austrian Open with a fighting 4-6, 6-4, 7-5 defeat of American Steve Johnson on Sunday. Ferrer, who joins Roger Federer on five titles this year - the pair are second behind Novak Dkjokovic on nine - now stands in solid contention for one of the two remaining places in the eight-man field for the World Tour Finals starting November 15.

Ferrer joins Richard Gasquet on joint seventh in the race to London. But of those trailing the pair, none save Gasquet have a real chance of qualifying, as Frenchman Jo-Wilfried Tsonga, provisional ninth, is not playing next week.

Ferrer claimed the 25th trophy of his career as he defeated Johnson, who was playing in his first final.