World number one Serena Williams brushed past a weary Conchita Martinez 6-2, 6-2 on Thursday to reach the quarter-finals of the $1.3 million Family Circle Cup and extend her unbeaten run to 23-0.

Having opened the day with a 6-2, 6-4 second-round win over Italy's Tathiana Garbin, Martinez, twice a winner here, had little in reserve for Williams, who overpowered the 15th-seeded Spaniard to stay on course for her fourth title of the season.

The holder of all four Grand Slam titles, Williams will now take on sixth seed Jelena Dokic of Yugoslavia, who put out 13th-seeded Russian Elena Dementieva 4-6, 6-4, 7-5.

In other third round action, second seed Justine Henin-Hardenne of Belgium defeated 14th seed Nathalie Dechy of France 2-6, 6-3, 6-2 and third seed Lindsay Davenport downed 16th seed Clarisa Fernandez of Argentina 6-4, 6-4.

Fifth seed Daniela Hantuchova of Slovakia and unseeded Frenchwoman Mary Pierce both came through busy schedules on Thursday.

Hantuchova followed up a 6-2, 4-6, 6-3 victory in her rain-delayed second-round match with Russia's Tatiana Panova by ousting American Jill Craybas 7-6, 6-3 in a third-round encounter later in the day.

Pierce, who earlier caused an upset by knocking out seventh-seeded Russian Anastasia Myskina 6-4, 1-6, 6-2, also recorded two victories on the same day by sweeping past 10th-seeded South African Amanda Coetzer 6-3, 1-6, 6-0 in the third round.

Ashley Harkleroad won the all-American third-round clash with Meghann Shaughnessy, easing aside the 11th seed 6-2, 6-2.