World number one Justine Henin-Hardenne kept Conchita Martinez waiting for her 700th career win when she beat the Spaniard 2-6, 7-5, 6-3 in the third round of the Amelia Island championship in Florida on Thursday.

Sixteenth seed Martinez, who is within one victory of becoming only the seventh player in the Open Era to reach 700 wins, broke the Belgian three times in the opening set and was a break up in the second.

But Henin-Hardenne broke serve four times in the second to force a decider and Martinez's weak delivery could not hold up in the third set.

Henin-Hardenne now meets Vera Zvonareva in the quarter-finals after the eighth seed from Russia put out Switzerland's Patty Schnyder 6-2, 6-3.

Second seed Serena Williams enjoyed another good workout as she continued her return to competition after a knee injury, easing past Croatian Karolina Sprem 6-1, 7-5.

The American, who won the title on her first appearance of the year at the Nasdaq-100 Open last week, was broken three times in the second set but the outcome was never seriously in doubt.

Former world number one Williams next plays seventh seed Nadia Petrova in the last eight after the Russian beat Hungarian Petra Mandula 6-1, 6-4.

Third seed Amelie Mauresmo of France also went through with a 6-3, 6-4 win over Czech qualifier Barbora Strycova.

Lindsay Davenport, seeded four, will have to return on Friday to complete her third-round clash with Australia's Alicia Molik. The American was leading 6-4, 5-5 when the match was suspended for the day.