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.
Williams, the two-time defending champion who has claimed five of her 17 Grand Slam singles titles at Flushing Meadows, was playing in her first major quarter-final of 2014.
She stretched her perfect record against Pennetta to 6-0, denying the Italian's bid to match her best Grand Slam performance - a semi-final run in New York last year.
In the battle of two 32-year-olds, Pennetta 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 roll of five straight games to finish it off in 63 minutes.
"I'm just so happy to have won," Williams 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."
Results on Wednesday from the 10th day of the US Open, the final Grand Slam tournament of 2014 (x denotes seeded player):
Novak Djokovic (SRB x1) bt Andy Murray (GBR x8) 7-6 (7/1), 6-7 (1/7), 6-2, 6-4
Kei Nishikori (JPN x10) bt Stanislas Wawrinka (SUI x3) 3-6, 7-5, 7-6 (9/7), 6-7 (5/7), 6-4
Serena Williams (USA x1) bt Flavia Pennetta (ITA x11) 6-3, 6-2
Ekaterina Makarova (RUS x17) bt Victoria Azarenka (BLR x16) 6-4, 6-2
Ivan Dodig/Marcelo Melo (CRO/BRA x4) bt Carlos Berlocq/Leonardo Mayer (ARG/ARG) 3-6, 6-4, 6-2
Marcel Granollers/Marc Lopez (ESP/ESP x11) bt Alexander Peya/Bruno Soares (AUT/BRA x2) 7-6 (7/3), 6-4
Kimiko Date Krumm/Barbora Zahlavova Strycova (JPN/CZE) bt Andrea Hlavackova/Zheng Jie (CZE/CHN x8) 6-3, 4-6, 6-3
Abigail Spears/Santiago Gonzalez (USA/MEX) bt Taylor Townsend/Donald Young (USA/USA) 6-3, 6-4
Sania Mirza/Bruno Soares (IND/BRA x1) bt Chan Yung-Jan/Ross Hutchins (TPE/GBR) 7-5, 4-6, 10-7