The Serena Slam will have to do for now.

Serena Williams, attempting to win the first calendar-year Grand Slam in nearly 30 years, came up short in the semifinals of the U.S. Open, losing to unseeded Roberta Vinci on Friday afternoon.

Vinci, ranked No. 43 heading into the final major tournament of the year, stunned the world's No. 1 player, 2-6, 6-4, 6-4.

Williams had won 33 straight matches at the majors before stumbling against Vinci, a streak that goes back to the 2014 U.S. Open. She won that major, along with the 2015 Australian Open, French Open and Wimbledon to give her a second career "Serena Slam."

But the Grand Slam drought in women's tennis will continue into 2016. Steffi Graf last accomplished the feat in 1988.

Asked if she thought this moment could be possible when she woke up Friday morning, Vinci said, "No."

Vinci faces fellow Italian Flavia Pennetta in the final on Saturday afternoon. Pennetta, 33, reached her first Grand Slam final by upsetting No. 2 Simona Halep in the earlier semifinal.

Vinci, ranked No. 43 in the world, broke Williams' serve in the fifth game of the second set to take a 3-2 lead. Vinci held off several break points the rest of the set and won it, 6-4, forcing a decisive third set.

It was the 11th time Williams went to a third set in a major this season.

In the third set, Williams picked up the early service break of Vinci for a 2-0 lead, but gave it right back by double-faulting on game point.