Serena Williams’ quest for a calendar-year grand slam came to a stunning conclusion Friday when she was defeated after three sets by Roberta Vinci, an unranked Italian player.

Vinci, who was a 300-to-1 underdog, defeated Williams in 6-2, 4-6, 6-4 sets on Friday in what could go down as the most shocking upset in tennis history.

Williams was attempting to do something that hasn’t been done in 27 years, win every major grand slam tournament in women’s tennis in a 12-month-span. Her loss to Vinci comes just days after a dramatic victory over her own sister, Venus Williams.

A physically-drained Vinci called the victory “the best moment of my life.”

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She apologized to the “American people and Serena” for any disappointment they might feel but said “today is my day.”

Williams later conceded that she made “more unforced errors than I normally make,” but added that her defeat was really due to the fact that Vinci “played literally out of her mind.”

“She didn’t want to lose today and, incidentally, neither did I,” Williams said.

Among those let down was Williams’ rumored boyfriend, hip-hop star Drake, who some sarcastic social media users blamed for the 33-year-old tennis icon’s loss. Other famous figures, including first lady Michelle Obama, expressed admiration for Williams’ achievement, despite coming up short.

So proud of you, @SerenaWilliams. What you did this year was amazing. -mo #USOpen2015 — The First Lady (@FLOTUS) September 11, 2015

So, I am devastated and stunned. We love you @serenawilliams so much. Sending lots of love always. #usopen2015 — Laverne Cox (@Lavernecox) September 11, 2015

For months, Williams has been under immense pressure to complete what was being dubbed the “Serena Slam” after winning the Australian Open, the French Open and Wimbledon. Tennis legend Steffi Gram was the last women’s tennis player to win all four grand slams in a row back in 1988.