A Ukrainian player upset Simona Halep in the first round of the U.S. Open.

Daria Snigur, 20, burst into tears after defeating Simona Halep of Romania, a two-time Grand Slam singles champion, in three sets on Monday in the first round of the U.S. Open.

Snigur, a Ukrainian who is ranked No. 124 in the world, was making her debut in the main draw of a Grand Slam singles tournament; she had to win three matches to qualify. Her win over Halep was her first career victory at the WTA Tour level.

“When I was in the moment, I didn’t understand what happened,” Snigur told reporters after the match. “I think it was the best match in my career.”

After Snigur’s win, her father, who was in the stands, put his hands on top of his head as if in disbelief.

“My father didn’t understand, too,” Snigur said.

Halep, the No. 7 seed, is coached by Patrick Mouratoglou, Serena Williams’s former coach. Halep had been given 8-to-1 odds to win the tournament before it began, according to SportsBetting.ag.

“I had tickets tomorrow to Warsaw,” Snigur said.

After shaking hands with Halep and the chair umpire, Snigur stepped back onto the court to wave at the crowd. She made a heart shape with her hands over a yellow-and-blue ribbon affixed to her top, a tribute to her country in the midst of war.

“Ukraine is always in my heart,” Snigur said of the gesture. “This victory is for Ukraine.”

While her father was able to travel with her for the tournament, Snigur said that her mother was still in Kyiv, Ukraine’s capital. Leading up to the U.S. Open, Snigur said she trained in the Latvian capital of Riga because the tennis facility she used in Ukraine had been bombed by Russian forces.

“Sometimes it’s impossible to play, but I try to do my best,” Snigur said. “I try to do the best for Ukraine. I try to support my country.”