An unimaginable Wimbledon run for 15-year-old Coco Gauff came to a disappointing end Monday.

The American tennis phenom lost to former No. 1 Simona Halep 6-3, 6-3 in the round of 16. Halep broke Gauff five times and took advantage of 29 unforced errors.

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Gauff was able to save two match points when serving at 5-2, but Halep clinched the victory when Gauff sent a forehand wide in the next game.

Gauff came into the event as the youngest competitor to make a Wimbledon draw in the Open era. She stunned the world when she defeated Venus Williams in the opening round, Magdalena Rybaikova in the second round and Polona Hercog in the third round.

Tennis legend Billie Jean King tweeted her congratulations to Gauff after the loss.

“Your journey is far from over, @CocoGauff. Looking forward to watching your future successes on the court and off,” King wrote.

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With the win, Halep reaches the Wimbledon quarterfinals for the fourth time and will face Zhang Shuai next.

The Associated Press contributed to this report.