One-time U.S. Open champion ​​Bianca Andreescu has no patience for hecklers. 

During her first-round match at the Mubadala Citi D.C. Open on Monday, the 23-year-old tennis pro shouted in frustration at a fan who reportedly kept having outbursts after she missed a serve.

Bianca Andreescu hits a forehand

Bianca Andreescu hits a forehand against Marta Kostyuk on day three of the Mubadala Citi DC Open at Fitzgerald Tennis Stadium. (Geoff Burke-USA Today Sports)

The last straw seemingly came in the third set with Andreescu and Ukraine’s Marta Kostyuk tied at 2-2. 

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The line judge ruled Andreescu’s serve out and, just moments later, the heckler could be heard shouting, "Out." 

"Shut up!" she shouted with her arms out by her side. 

The chair umpire was seen reaching for her radio, likely to call security. According to the New York Post, Andreescu refused to continue play until the heckler was removed from the stadium.

Bianca Andreescu reacts to a missed shot

Bianca Andreescu reacts after missing a shot against Marta Kostyuk during the Mubadala Citi DC Open at Fitzgerald Tennis Stadium. (Geoff Burke-USA Today Sports)

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Andreescu lost the match 2-6, 6-3, 7-6(5) and took to social media after to share her feelings about the day. 

"What a wonderful sport," she tweeted out. 

Bianca Andreescu plays win the Mubadala Citi DC Open

Bianca Andreescu hits a volley against Marta Kostyuk at the Mubadala Citi DC Open. (Geoff Burke-USA Today Sports)

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Kostyuk battled back from one set down and saved three match points to defeat 44th-ranked Andreescu. 

"I lost my chances at 4-all, there were some painful mistakes," Kostyuk said after the match 

"Honestly, I didn't believe I could win this one but I was just trying to play every point and stay in the match and fight, not give up."