• Serena Williams

Serena Williams (Photo : REUTERS )

Tennis star Serena Williams will have to wait yet another year to secure a historic calendar Grand Slam. After looking promising all tournament, she has been defeated in a major upset by Roberta Vinci in the semi-finals of the 2015 U.S. Open.

Roberta Vinci defeated Serena Williams (2-6, 6-4, 6-4)

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Serena won the first set and looked to be in good form to walk over her opponent. However, she dropped the second set and it all went downhill from there. According to a match report by BBC, she completely boiled over in the deciding set. "I don't want to talk about how disappointing this is for me," she said in her post-match press conference.

Up until the semi-final match against the Italian, Serena's biggest threat appeared to be her sister, Venus. The siblings met in the quarterfinals on Tuesday, where Serena defeated her older sister after three sets (6-2, 1-6, 6-3).

With Venus out of the way, Serena was the clear favorite to reach the final. Her semi-final opponent was the unseeded Vinci and she appeared to be small fry next to the current World Number 1. Williams has 69 singles titles under her belt and was going for a calendar Grand Slam. Vinci meanwhile, was setting foot in a Grand Slam semi-fial for the first time.

Unfortunately for Serena, history was not to be made this year. According to USA Today, her coach said that she lost her way "mentally" and "tactically" during the match against the unheralded Italian.

"Players are humans. How many times did it happen this year where she felt like this and she still found her way through? She didn't find her way today." he said, after explaining that Serena felt off when she woke up on Friday.

The match was originally scheduled for Thursday evening, but was postponed for Friday after facing a rain suspension. Would it have made a difference for Serena if the match was played on thursday? No one will ever know.

In the end, it will be Vinci, first-timer in a Grand Slam final, who could make history. Her opponent, fellow Italian Flavia Pennetta, is also seeking her first Grand Slam Singles Title. The pair will face off on Saturday, Sept, 12.