World number one Serena Williams has missed out on the chance to complete the calendar Grand Slam after Italy's Roberta Vinci came from a set down to win 2-6 6-4 6-4 in the semi-finals at the US Open.

The 21-time Grand Slam champion found herself down a break of serve early in the first set, but soon got back on level terms, breaking back in the following game.

The world number one seemed to be cruising towards a spot in the final as she picked up the next four games, breaking Vinci twice more to swiftly wrap up the opening set.

Williams pushed the Italian at the start of the second set as she looked to win a seventh straight game in the match, but her unseeded opponent battled to keep the set level, before taking advantage of a string of errors from the defending champion to go a break up and levelling the match a couple of games later.

The American appeared to have upped her game at the start of the deciding set as she immediately broke her opponent, but Vinci fought back once again as Williams made a double fault.

At 3-3, two more double faults from the world number one gave Vinci a chance to edge in front, and she converted her second break point, giving her the chance to serve for the match shortly after, sealing her place in tomorrow's final with a volley.

Vinci will face compatriot Flavia Pennetta in the final after she upset world number two Simona Halep earlier on Friday, also reaching a Grand Slam final for the first time in her career.