SINGAPORE — Caroline Wozniacki credited her training for next month’s New York Marathon as a key factor in her victory over Maria Sharapova in a grueling three-set match in the WTA Finals on Tuesday.

Wozniacki won 7-6 (4), 6-7 (5), 6-2 to beat Sharapova for the second-straight time, having also won in the fourth round of the U.S. Open. Tuesday’s result in the round-robin match dealt a major blow to Sharapova’s hopes of claiming the year-end No. 1 ranking.

Wozniacki, who has always been regarded as one of the fittest players on tour, said her additional running work in preparation for the marathon had taken her stamina to a new level and also given her added belief in Tuesday’s 3 hour, 15-minute match.

No such stamina was required in Tuesday’s other match as Agnieszka Radwanska had a comfortable 6-2, 6-3 win over Wimbledon champion Petra Kvitova.

Valencia Open

ROBREDO BEATS NO. 5 SEED ISNER: In Valencia, Spain, Tommy Robredo advanced to the second round of the Valencia Open by beating fifth-seeded John Isner 7-6 (3), 6-3 on Tuesday.

Robredo saved five break points to force a first-set tiebreaker, which he dominated and won after the American netted a forehand.

Robredo had no unforced errors and broke Isner before serving out the match at love.

The Spaniard will next play Yen-Hsun Lu of Taiwan.

Also, fourth-seeded Feliciano Lopez moved past qualifier Norbert Gombos 6-4, 6-4 and will play Pablo Carreno Busta next.

Alexandr Dolgopolov of the Ukraine ousted eighth-seeded Gilles Simon 6-0, 6-3 with 10 aces, and broke the Frenchman five times.

Dolgopolov will now meet another Frenchman, Jeremy Chardy, after he brushed aside Tunisian qualifier Malek Jaziri 6-2, 6-1.

Fernando Verdasco outlasted Argentine Leonardo Mayer 6-4, 3-6, 6-3. Verdasco will play the winner of the match between top-seeded David Ferrer and Andreas Seppi.

Dusan Lajovic of Serbia also won his opener and will face either second-seeded Tomas Berdych or Pablo Andujar.

Swiss Indoor

No. 4 seed Raonic wins; Wawrinka upset: In Basel, , Switzerland, fourth-seeded Milos Raonic hit 12 aces and saved all five break points he faced as he beat Steve Johnson of the United States 7-6 (4), 6-4 in the first round of the Swiss Indoors on Tuesday.

Mikhail Kukushkin upset third-seeded Stanislas Wawrinka of Switzerland 6-4, 6-7 (1), 6-3 later Tuesday. The 84th-ranked Kazakh converted four of his 10 break chances to set up a second-round match with Germany’s Benjamin Becker, who needed just over one hour to breeze past qualifier Gastao Elias of Portugal 6-3, 6-2.

Meanwhile, eighth-seeded Ivo Karlovic had 23 aces as he advanced to the second round with a 7-6 (4), 6-3 win against Lukas Rosol.

The 35-year-old Karlovic won 95 percent of his first-serve points and next plays Frenchman Kenny De Schepper, who beat Argentina’s Federico Delbonis 7-6 (3), 7-5.

Croatia’s Ivan Dodig needed nearly three hours to get the better of Swiss wild card Marco Chiudinelli 6-4, 6-7 (7), 6-4 and next plays seventh-seeded David Goffin of Belgium.

Canada’s Vasek Pospisil needed just under two hours to defeat Jarkko Nieminen of Finland 6-3, 6-7 (4), 6-4 in the late match. The 24-year-old Pospisil next faces fifth-seeded Grigor Dimitrov or German wild card Alexander Zverev.

Top-seeded Roger Federer and No. 2 Rafael Nadal, who struggled with appendicitis earlier this month in Shanghai, are in second-round action on Wednesday.