Serena Williams continued her dominant run at the U.S. Open, dispatching Ana Ivanovic 6-1, 6-3 to enter the semi-finals at Flushing Meadows.

Williams is the last American left in the tournament after Andy Roddick's loss to Juan Martin Del Potro, and the 30-year-old was at her usual best.

Ivanovic came into the match, knowing she would need to be at her best and stay aggressive to stand any chance of pulling off a victory against the in-form Wimbledon and Olympic champion. It is easier said than done though. The 30-year-old slammed 12 aces and hit 26 winners overall as she continued her march in the final grand Slam without dropping a single set.

"I feel like I'm going to get more focused and serious and start playing Serena tennis in the next couple of rounds, if I get to play two rounds. That's my goal," Williams said.

"I didn't think I came into this tournament playing my best, but I definitely played better in the last two matches.

"I felt much better moving. I was excited I'm moving faster. Feels good. I felt solid."

Williams will face Sara Errani in the final-four match, after the Italian beat her best friend and doubles partner Roberta Vinci 6-2, 6-4.

"She (Errani) is playing well," Williams observed. "She made the final at Roland Garros and now semis here, potential finals, so I can't underestimate her.

"It's not by luck she's been doing so well. We will have to see."

Errani added: "A lot will depend on her. I will try to play my game, try to get her off balance. I still need to study up and prepare."

Ivanovic was reasonably satisfied with her performance, after reaching her first quarterfinal in a Grand Slam in four years. "Overall I'm very satisfied," the former world number one said. "I played some really good tennis to get into this position.

"Even tonight I felt like I was striking the ball so nicely on both sides.

"That's something that I worked hard for. I think it's a big step for me to reach quarterfinal. It's a confidence boost."

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