CHARLESTON, S.C. -- Serena Williams only had three days to make the transition from hard courts to clay, and it showed a few times as she won her opening match at the Family Circle Cup.

The world's No. 1 player beat Camila Giorgi 6-2, 6-3 on Tuesday, losing her serve in her second game and looking uncomfortable when the Italian was able to get Williams running.

"It was definitely not great for me. I think I played well, but I wasn't great footing-wise. I was just trying to get my stability," Williams said.

Williams avoided a rash of upsets at the first clay court tournament of the season. Three of the top seeds were beaten in their opening matches, including No. 4 Sloane Stephens, who lost 6-2, 6-0 to Bethanie Mattek-Sands.

Williams did look shaky to start. Up 3-2 in the first set, she was nearly broken again. She lost the first three points of the game before rallying back to win the next five. Giorgi wouldn't get another chance to break Williams the rest of the match, and only won two points against Williams' serve the entire second set.

Williams said she figured she would start slow because she only got one day of practice on clay to adjust from the fast, hard surface at Key Biscayne where she won the title for the sixth time Saturday to the green, slow clay in Charleston, where she is the top seed.

"It was a little awkward for me," said Williams, who at 31 is the oldest woman to ever have the world's top ranking.

She also was facing a 21-year-old rising star in Giorgi, who caught Williams' eye last year by making it to the fourth round at Wimbledon.

"I actually have been watching her. I think she is a good player and I knew one day I'd be playing her," Williams said.

Giorgi had only herself to blame for not taking advantage of Williams' slow start. She had eight double-faults in the first set and 12 for the match. Williams' broke serve in the first two games as Giorgi's second serves went into the net each time.

Williams advances to the third round and just as importantly gets a day off Wednesday. She said she plans on hitting just a few balls, but mostly resting. And if last year is any indication, Williams should get stronger as the tournament goes on. Williams won her opener 6-3, 6-4 in the 2012 tournament, and then lost seven games the rest of the week.

Another player glad to have a day off is Mattek-Sands. She beat Stephens in 57 minutes, one day after her three-set opening match win went 3:42, the longest WTA match this season.

Mattek-Sands pounced on Stephens, breaking her in the fourth game of the match.

"I was able to string some games together and get under her skin a bit," said Mattek-Sands, who slept for 12 hours after her marathon match, then took a four-hour nap before the Tuesday evening session.

Stephens struggled to place her shots, consistently hitting it just long or outside. She has never won a match in Charleston in three tries, but still said she was surprised she played so badly Tuesday night.

"She played well and I really couldn't find a rhythm," Stephens said. "The balls were going everywhere

The other upsets Tuesday included qualifier Jessica Pegula, whose father Terrence owns the Buffalo Sabres, beating No. 8 seed Mona Barthel 7-6, 6-1. Seventh-seeded Carla Suarez Navarro lost to Stefanie Voegele 6-2, 6-4 and qualifier Vania King defeated No. 14 seed Yaroslava Shvedova 4-6, 6-1, 6-4 and .

All the other seeded players won Tuesday, including No. 9 seed Jelena Jankovic who beat Melanie Oudin 6-4, 5-7, 6-4 in a match that took nearly three hours. It was Jankovic's first win over Oudin in three matches.

"She has this game that I really don't like and doesn't really suit me," Jankovic said. "I always have trouble with her."

Jankovic, who won in Charleston in 2007, wasn't the only former Family Circle Cup champion to win Tuesday. No. 15 seed Sabine Lisicki, the 2009 winner, beat Anna Tatishvili 6-0, 6-0.

"It's nice to play on the clay court," Lisicki said. "The quick turnaround is not always easy, but I love the green clay."

Other seeded players to advance were No. 10 Julia Goerges, No. 11 seed Sorana Cirstea, No. 12 seed Varvara Lepchenko and No. 16 seed Laura Robson.

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