World number one Serena Williams [ Images ] 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 [ Images ] 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 [ Images ] of Yugoslavia, who put out 13th-seeded Russian Elena Dementieva [ Images ] 4-6, 6-4, 7-5.

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

Fifth seed Daniela Hantuchova [ Images ] of Slovakia and unseeded Frenchwoman Mary Pierce [ Images ] 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 [ Images ] 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 [ Images ] 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.