Serena Williams is still struggling to get over a defeat almost 10 years after it took place.

The legendary tennis player did not lose very often throughout her illustrious career, as her 23 Grand Slam titles and 319 weeks as World number one illustrates.

But there was one particular defeat Serena Williams suffered that is remembered as one of the biggest upsets in tennis history.

The 42-year-old created many pieces of history during her playing days but she was denied the chance to possibly create more on a fateful day in 2015.

Which defeat did Serena Williams struggle to move on from?

Certain losses will hurt more for the greatest athletes given they are few and far between.

This was certainly the case for Williams, who was on course to win all four Grand Slams in the same year back in 2015.

Serena Williams of the United States reacts in the second set against Ajla Tomlijanovic of Australia during their Women's Singles Third Round match...

She entered that year’s US Open semi-final against Italy’s Roberta Vinci as the overwhelming favourite, but she suffered a shocking 6–2, 4–6, 4–6 loss.

This ended her chances of becoming the first person since Steffi Graf in 1988 to complete the calendar-year Grand Slam.

Years later, that loss still bothers Williams and she elaborated on it during her ESPN+ documentary series titled ‘In the Arena’.

“It doesn’t in the way it does in the movies and no matter how much I feel like it could and should no matter how much I do different, it wasn’t my story,” she said.

“Winning is so glamorous and everyone thinks it’s so amazing when you win. But the more you win, the harder it is to lose.

“I don’t think I was able to move on from that US Open loss. I was just so angry and so sad and so disappointed with myself.

Said no-one with 21 Grand Slams at that time, but it wasn’t enough for me.”

Serena Williams of the U.S. after missing a return from Roberta Vinci of Italy in their semi-final match at the U.S. Open tennis tournament in New ...
Photo by Gary Hershorn/Corbis via Getty Images

What did Serena Williams win after that 2015 US Open defeat?

Though Williams said she was haunted by the 2015 US Open loss to Vinci, she rebounded in empathic fashion on court.

The following year she reached the Australian Open final and suffered a narrow 4-6, 6-3, 6-4 defeat to Angelique Kerber, before the pair met again in the Wimbledon final five months later.

Williams exacted some revenge on Kerber and claimed her 22nd major and seventh at the All-England Club.

Serena then began 2017 by going one step further than the year before and won the Australian Open title.

Serena defeated sister Venus Williams to her 23rd and final major, all while pregnant with her first child Alexis Olympia.