Saturday’s Family Circle Cup semifinal between Serena Williams and Samantha Stosur had the air of a heavyweight fight.

For about 15 minutes.That’s how long it took Williams to seize control. She won the first eight points and cruised to a shocking 6-1, 6-1 victory over Stosur, ranked No. 5 in the world and the reigning U.S. Open champion.

The Stadium Court crowd had barely settled in their seats before Williams, ranked No. 10, had broken Stosur’s serve three times and established her dominance. Her win took only 59 minutes and left Stosur smiling ruefully at the end.

“It didn’t really seem to matter what I did,” said Stosur, who beat Serena in the U.S. Open final last year, and won the Family Circle Cup title in 2010. “She came out with the goods every time.”

Williams, the 2008 Family Circle Cup champ, said it was one of the best days of her career, which includes 39 WTA singles titles and 13 Grand Slam championships.

“I have to say, this is probably the best match I’ve played in my career, either in a long time or it’s up there in the top five,” said Williams, who will be a heavy favorite over 25th-ranked Lucie Safarova in today’s final. The stats backed up Serena, who exacted revenge for Stosur’s 6-2, 6-3 win in the U.S. Open, and for the Aussie’s three-set victory over big sister Venus Williams in Friday’s quarterfinals.

Serena smacked seven aces, including one at 122 mph, and won 21 of 23 points when she got her first serve in. Stosur managed only two break points, and Serena won them both. And Serena’s return game was just as good.

“She really didn’t allow me to almost take a breath when I was serving,” Stosur said. “Before I knew it, the ball was back on me.”

Serena’s biggest worry now? Peaking too early, before the French Open this summer.

“I was really relaxed out there,” said Serena, who is 30. “And I love that I’m playing some great tennis in my career at this point.”

Serena’s joy showed through when she executed a double pirouette after a swinging volley winner in the second set.

“That’s the shot I hit with my eyes closed,” she said. “I didn’t mean to spin, but I was on the clay and I kept spinning. I was like, oh my God, this is so embarrassing. I hope nobody remembers this.”

Stosur, for one, will try to quickly forget this beatdown. It was the exact opposite of the sizzling performance she put on in a 6-0, 6-3 blitzing of Vera Zvonareva in the 2010 FCC finals.

Stosur played 3½ hours on Friday, finishing off her rain-delayed third-round match before battling Venus Williams. Meanwhile, Serena had an easy walkover against Sabine Lisicki, who rolled her ankle trailing 4-1 in the first set and withdrew.

“I actually felt pretty good out there,” Stosur said. “My body, I wasn’t aching or really all that tired, to be honest with you. So unfortunately, I can’t use that as an excuse.”

Storur, 28 and one of the fittest players on the WTA Tour, changed tactics in desperation, trying a bit of everything — baseline, net, slice. Nothing worked.

“It’s hard, when you’re not really getting into that many rallies,” she said. “It’s hard to really break into something until you can maybe extend the points.

“I tried doing that, but it wasn’t to be.”