It will be Williams vs Williams in semis

Serena Williams returns to Lucie Safarova during her 6-4, 6-1, victory at the Family Circle Cup in Charleston, SC, on Friday. [Photo/Agencies]

Top-ranked Serena Williams and sister Venus both won twice on Friday to reach the Family Circle Cup semifinals and set up their first sibling showdown since 2009.

Serena won her 13th straight match by defeating sixth-seeded Lucie Safarova, 6-4, 6-1. Earlier, she topped Mallory Burdette in a third-round match moved due to Thursday's 7-hour rain delay.

Venus also had double duty, downing Varvara Lepchenko in three sets before ousting Madison Keys later on Billie Jean King Court.

The Williams sisters next go for a spot in the finals. They haven't met in a tournament since the 2009 Tour Championships in Qatar. Serena holds a 13-10 lead, although they're 1-1 on clay.

"For the record, we've never played two matches on the same day," Serena told the stadium crowd. "You guys had a real treat."

The sisters were the first four matches on the stadium court - and they only dropped one set combined.

"It was a quadruple-header," Venus said with a laugh. "I don't know if that's ever going to happen again."

Serena is seeking her third Family Circle title after wins in her past two appearances in 2008 and 2012. Venus took this title in 2004 and scored the clinching points last September when the Washington Kastles took the World Team Tennis crown at Family Circle Tennis Center.

Serena, 31, comes in as world No 1, having won Wimbledon, the Olympics and the US Open since capturing last year's Family Circle. She added to her haul with a sixth Sony Open crown, rallying past Maria Sharapova for her 48th career WTA crown.

Venus has struggled with illness and injury in recent years. She took six months off after being diagnosed with Sjrogen's Syndrome, an autoimmune disease, and withdrew from the Sony last month because of a sore back.

Still, Serena is wary of her sister's game and desire to win. "When I play Venus, it's never an easy opponent," she said.