MIAMI, Florida (AFP) — World number one Serena Williams reached the semi-finals and British second seed Andy Murray booked a quarter-final berth with straight-set triumphs yesterday at the WTA and ATP Miami Masters.

Williams defeated Chinese fifth seed Li Na 6-3, 7-6 (7/5) while Murray downed Italian 16th seed Andreas Seppi 6-2, 6-4 at the $8.5 million hardcourt tournament.

World number one Novak Djokovic of Serbia was due to meet German 15th seed Tommy Haas in a later fourth-round match yesterday.

Breaking Li three times in each set, Williams fell behind in the second set before roaring back to hold off Li, taking the last point off the Chinese’s star’s serve to end matters after one hour and 50 minutes.

“It’s good to be able to at least come back,” Williams said. “I like to believe that I try to be a solver. I just try to do things different if something is not working”.

Williams had three aces and six double faults to one ace and seven double faults for Li.

Williams improved to 7-1 against Li with her sixth victory in a row, Li’s only win coming at Stuttgart in 2008.

Williams, trying to become the first six-time winner in Miami history, will face either defending champion and fourth seed Agnieszka Radwanska of Poland or 30th-seeded Belgian Kirsten Flipkens.

Williams won Miami titles in 2002, 2003, 2004, 2007 and 2008.

The 15-time Grand Slam champion also captured last year’s US Open, Wimbledon and Olympic crowns.

Li made a strong return to the tour at Miami after an ankle injury suffered in losing the Australian Open final. Li said the ankle felt “100 per cent” after the match but wished she could have served better against Williams.

Scotsman Murray, the 2009 Miami winner who lost to Djokovic in last year’s Miami final, needed only 86 minutes to book a date in the last eight against the winner of a later match between French sixth seed Jo-Wilfried Tsonga and Croatian

ninth-seed Marin Cilic.

In the men’s draw Spanish third-seed David Ferrer advanced to the quarter-finals with a 6-4, 6-2 victory over Japan’s 13th-seeded Kei Nishikori.

Ferrer won 84 per cent of his first-serve points and 5-of-9 break chances to eliminate Nishikori and book a last eight-date against Austria’s Jurgen Melzer, who defeated Spain’s Albert Ramos 2-6, 6-3, 6-3.

Fifth-ranked Ferrer improved to 3-2 in his meetings with Nishikori, having avenged a round-of-16 loss at the Olympics by defeating the Japanese player in the fourth round of this year’s Australian Open.

French eighth-seed Richard Gasquet outlasted Spanish 10th-seed Nicolas Almagro 6-7 (3/7), 7-5, 7-6 (7/3) and will next face Czech fourth seed Tomas Berdych, who dispatched US 17th seed Sam Querrey 6-1, 6-1.