New York: Serena Williams roared back from an early deficit to defeat Flavia Pennetta 6-3, 6-2 on Wednesday and book a US Open semi-final clash with Ekaterina Makarova.
Playing in her first Grand Slam quarter-final of 2014, world number one Williams kept her bid for a third-straight US Open title -- and sixth overall -- alive as she stretched her perfect record over the 11th-seeded Italian to 6-0.
"I'm just so happy to have won," the 17-time Grand Slam champion said, noting that she'd had a "tough year" in the majors.
"It feels so special to be back in a semi-final, especially in New York."
In Makarova she'll face a first-time Grand Slam semi-finalist.
The 17th-seeded Russian advanced with a 6-4, 6-2 victory over former world number one Victoria Azarenka -- runner-up to Williams the past two years.
"I'm feeling amazing -- finally I'm in a semi-final," said the Russian left-hander, who had failed in four prior major quarter-finals. "It's a great feeling."
In a battle of two 32-year-olds, Williams denied Pennetta a repeat of her best Grand Slam performance -- a semi-final run in New York last year.
But the Italian gave Williams some tense moments in the early going, seizing a 3-0 lead with two breaks of serve in just eight minutes.
World number one Williams responded by winning the next six games to take the first frame in less than half an hour.
Serving for the set, Williams found herself facing double break point after a second double fault of the game, but reeled off the next four points to avert the danger.
"I felt she was playing really well," Williams said of Pennetta's fast start. "I don't think I was doing too much wrong."
Pennetta stopped the rot in the opening game of the second, fighting off a break point with her first ace of the match and securing the game with her second.
Williams held in the next, saving two break points in a game that went to deuce three games and finishing off with back-to-back aces.
It was Pennetta's turn to fight off a break with a brace of aces in the next, but that would be her last hurrah.
Williams held with ease in the next game, starting a streak of five straight games to finish it off in 63 minutes.
"You have to believe you can win all the time," Pennetta said. "I got on the court and tried to do what I have to do to bring the match home, but she was really good today.
"I think we played really good tennis tonight, really strong tennis."
Although Makarova is in the final four of a Grand Slam for the first time, she goes in knowing she has beaten Williams on one of the game's biggest stages -- in the fourth round of the 2012 Australian Open.
The left-hander from Moscow recovered an early break in the first set, breaking Azarenka twice in each frame to break through after four Grand Slam quarter-final defeats.
- Azarenka out-played -
Shortly after the match, Azarenka's spokesman told reporters that the player had suffered food poisoning and had been vomiting in the run-up to the quarter-final.
But Azarenka said she was just out-played.
"I'm not going to make excuses for myself. I did the best I could today," Azarenka said. "I want to give full credit to my opponent. She deserves to win. She played much better than me today."
Makarova, who evened her head-to-head record with Azarenka at three matches apiece, said she didn't notice any drop-off in the Belarusian's game.
"I think she played the same, so aggressive," Makarova said. "At the beginning it was really tough to change the game to my way because she was really aggressive and let me move a lot.
"Then she did the break, and I just tried to stay with my game, to play point by point, to be solid and turn it around."
The other women's semi-final was set on Tuesday, with former world number one and 2009 runner-up Caroline Wozniacki, the 10th seed, booking a meeting with unseeded Chinese Peng Shuai.
Peng, like Makarova, is in a Grand Slam semi-final for the first time, joing Li Na and Zheng Jie as the only Chinese to make it so far at a major.