Serena Williams' bid for a rare calendar-year Grand Slam came to a shuddering halt on Friday when the three-times defending US Open champion suffered a stunning 2-6, 6-4, 6-4 loss to unseeded Italian Roberta Vinci.

For world number one Williams, who was bidding to become only the fourth woman to win all four majors in the same year, was left frustrated by the Italian's defense and creativity in the final two sets.

32-year-old Vinci was in her first ever Grand Slam semifinal, but overcame all the odds to end Williams' 33-match streak of Grand Slam victories. The victory means the women's US Open final will be contested by the first ever Italian women to make the final in the open era.

Vinci faces fellow Italian Flavia Pennetta after the 26th-seed stunned second-seed Simona Halep 6-1, 6-3. "I never thought I would get this far," said Pennetta afterwards. Halep, who made last year's French Open final, had 23 unforced errors to 10 winners and looked just as tired as the stats suggest. 33-year-old Pennetta showed her experience and was not overwhelmed on the big stage having reached at least the quarterfinals at Flushing Meadows in six of the last seven years.

Djokovic-Federer Final

Later on Friday, the men's semi-finals matches were both finished in three sets. World number one Novak Djokovic beat defending champion Marin Cilic 6-0, 6-1, 6-2.

"I haven't been very successful in the finals of the US Open," Djokovic said. "I have won one and lost four but have been playing some of my best tennis on these courts."

Roger Federer, ranked just behind the Serbian player, beat Stan Wawrinka 6-4, 6-3, 6-1.

"I’m very happy, it’s been a great tournament so far," Federer said. “I tried very hard in the last six years to get to another final, I came close a few times and tonight it worked against Stan, who also played a good tournament."

Djokovic and Federer will meet in Sunday's final for their 42nd match. To date Federer has won 21 times and Djokovic 20 times.

jh/bw (Reuters, dpa)