Maria Sharapova continued her mastery of Romania's Simona Halep with a high quality 6-4, 6-4 victory filled with bruising baseline rallies to edge closer to a last four berth at the WTA Finals on Tuesday.
The Russian world number four topped the Red Group at the eight women end-of-season finals with her second win and next faces U.S. Open champion Flavia Pennetta, who said she would retire after the tournament, with a semi-final spot on the line.
The 28-year-old Russian, who had won all five previous matches against Halep, was controlling the bulk of the rallies from the centre of the court with some rangy defensive work also causing the Romanian angst.
The 33-year-old Italian had earlier kept alive her WTA Finals bid with a flurry of backhand winners as she downed a strapped up and fatigued Agnieszka Radwanska 7-6(5), 6-4 to leave the Pole bottom of the standings with two defeats.
It was Pennetta's first win in the group -- she was blown away by top seed Halep 6-0 6-3 in her opener on Sunday -- with her backhand proving a particularly devastating weapon at the Singapore Indoor Stadium.
Sharapova's win over the Romanian means all four players in the group still hold hopes of grabbing one of two semi-final spots available and Pennetta said she had been impressed by the Russian, who has been hit with injury problems since Wimbledon.
"She has this adrenaline because she was out for three or four months, something like that," the Italian told reporters. "When you come in the court after so long you are with a lot of energy. It's going to be tough for sure."
Sharapova edged Radwanska over three tough sets on Sunday but showed no willingness to go the distance again on Tuesday in a ferocious baseline battle against the top seeded Halep.
Both players traded early breaks with neither enjoying an easy ride on serve before five-times grand slam champion Sharapova secured the set by breaking Halep, runner-up here last year, for a second time at 5-4.
Sharapova, runner-up to Serena Williams at the Australian Open this year, broke Halep again in a lengthy second game of the second set and some blistering winners from both sides of the court allowed her to open up a 5-1 lead.
She looked set to serve out the match before her double fault demons returned as she was broken from 30-15 up and then lost her next service game as Halep fought back to be on serve.
Her recovery, though, was quickly ended by the shrieking Sharapova who broke in the next game to seal the match with a bruising backhand before letting out a roar of approval.