Czech tennis star Karolina Muchova needed to rally against her Romanian opponent, Sorana Crstea in the second round of the U.S. Open.Muchova was down 4-1 in the second set on Thursday when she needed to briefly halt the match. She began to get emotional and admitted after the match it was because she saw her ex-boyfriend sitting in the crowd.CLICK HERE FOR MORE SPORTS COVERAGE ON FOXNEWS.COMShe rallied to defeat Crstea in three sets."Well it wasnt tennis-related," she told reporters after the match, via The Athletic. "So l dont really like talking about it. But opposite my bench, my ex-boyfriend sat down. He sometimes shows up at places where he shouldnt be. That startled me a bit. I told him to leave, he didnt, but later he did go. It was hard to focus in that moment."Muchova hadnt mentioned the man to the Womens Tennis Association (WTA) or the United States Tennis Association (USTA) before the tournament began and hasnt done so after Thursdays incident, The Athletic reported.Tennis players can request certain spectators to be blacklisted from ticket sales or being able to receive credentials. An alleged stalker of Emma Raducanu appeared at the Dubai Tennis Championships in February. The man was blacklisted from purchasing tickets for Wimbledon.US OPEN SPECTATOR PROPOSES TO GIRLFRIEND DURING ARYNA SABALENKA'S WIN OVER LEYLAH FERNANDEZMuchova said Saturday after moving on to the round of 16 that she was doing well and didnt report the person to tennis officials."Player safety is a critical element of our planning and execution for the U.S. Open," a USTA spokesperson told the outlet. "Our comprehensive security plan includes protocols and procedures for effective risk mitigation and issue management. We work closely with the ATP, WTA, ITF, ITIA and the other Grand Slam events to stay informed of all relevant situations and concerns."The U.S. Open is in constant communication with local and federal law enforcement, who also maintain a presence at the USTA Billie Jean King National Tennis Center. We utilize both physical and technological means throughout the event to monitor and maintain security, including online threats to players."Muchova went as far as the semifinals at the U.S. Open two years in a row. She was ranked No. 13 going into the tournament.Follow Fox News Digitalssports coverage on X and subscribe to the Fox News Sports Huddle newsletter.