Drama built at Arthur Ashe Stadium around the upcoming match, postponed from Thursday by rain, between three-time defending champion Williams and Italy's 43rd-ranked Roberta Vinci, in her first Grand Slam semi-final.
Williams, on a 33-match Grand Slam win streak and a 26- match US Open win streak, is only two victories shy of completing two of the most incredible achievements in the history of tennis, playing her best tennis at an age once thought impossible for such success.
Williams, who is 4-0 lifetime against Vinci, owns a 7-0 career edge on 26th-ranked Pennetta, who took just 59 minutes to dispatch second-ranked Halep 6-1, 6-3 and reach her first Grand Slam final.
"It's amazing," Pennetta said. "I didn't think to be so far in the tournament. I played really well. I don't know how to handle all the inspiration I have.
Only five players have completed the calendar-year sweep of the Australian, US and French Opens and Wimbledon -- Americans Don Budge in 1938 and Maureen Connolly in 1953, Australians Rod Laver in 1962 and 1969 and Court in 1970 and Germany's Graf in 1988.
Williams, 53-2 this season, seeks her 70th career title. She is trying for a seventh US Open singles crown, an Open Era record and one shy of Molla Bjurstedt Mallory's all-time record, and a fourth US Open trophy in a row, matching Chris Evert for the Open Era mark.
