Andy Murray survived a test of his credentials to see off South Africa's Kevin Anderson in three sets and secure a place in the semi-finals of the Valencia Open.

The world No.10, chasing his second title in the Spanish city, had endured few problems in earlier wins over Jurgen Melzer and Fabio Fognini but found seventh-seed Anderson a different prospect.

Murray lost the opening set on a tie-break, but fought back bravely to claim a 6-7 (3/7), 6-4, 6-4 victory which kept the players on court for two hours and 43 minutes.

The slog may yet take its toll on third-seed Murray whose semi-final opponent and rival for an ATP Tour Finals slot, David Ferrer, raced past Brazil's Thomaz Belluci 6-1, 6-2.

The Spaniard will overtake Murray in the eighth and final Race to London slot if he beats him.

Meanwhile, Serena Williams reached the last four at Singapore's WTA finals and tied down the year-end world No.1 ranking without hitting a ball. Simona Halep, who inflicted Williams' heaviest defeat for 16 years on Thursday, tended the wound by stealing a set in defeat to Ana Ivanovic.

That was enough to usher Williams through to the BNP Paribas event's semi-finals, where she will meet Caroline Wozniacki.

Maria Sharapova botched three match points before regrouping to beat Angieszka Radwanska 7-5, 6-7 (7/4), 6-2 but the Pole sneaked through to meet Halep in the semi-finals, courtesy of Wozniacki's victory over Petra Kvitova.

"She owes me a handbag," Wozniacki said after helping Radwanska progress thanks to her 6-2, 6-3 win over Kvitova.