In a match between the last two U.S. Open champions, Sloane Stephens came out on top.

The 2017 champion beat Naomi Osaka 7-5, 4-6, 6-1 Monday at the WTA Finals, the season-ending tournament for the top eight players in the world.

Naomi Osaka of Japan returns a shot to Sloane Stephens of the United States during their women’s singles match at the WTA tennis tournament in Singapore on Monday, Oct. 22, 2018. (AP Photo/Vincent Thian)

Both players are making their debut appearances at the tournament, but Stephens appeared to be more composed while Osaka, who became the first Japanese citizen to win a Grand Slam title last month in New York, never seemed comfortable.

Naomi Osaka of Japan returns a shot to Sloane Stephens of the United States during their women’s singles match at the WTA tennis tournament in Singapore on Monday, Oct. 22, 2018. (AP Photo/Vincent Thian)

“I’m just really happy to get through and play a good competitive match,” Stephens said on court after the match. “I never gave up. I knew she’s been playing well and I’d have to play really good tennis to beat her.”

Sloane Stephens of the United States wipes her brows during a women’s singles match against Naomi Osaka of Japan at the WTA tennis tournament in Singapore on Monday, Oct. 22, 2018. (AP Photo/Vincent Thian)

Both players struggled to hold serve. Osaka was broken on seven of 19 break-point opportunities, while Stephens was broken on four of 12.

Stephens entered the tournament with 33 wins this season, the least of any of the eight qualifiers. She reached her second career Grand Slam final at this year’s French Open, and won the Miami title.

Naomi Osaka of Japan returns a shot to Sloane Stephens of the United States during their women’s singles match at the WTA tennis tournament in Singapore on Monday, Oct. 22, 2018. (AP Photo/Vincent Thian)

Osaka continually showed her frustration during the match. When she failed to capitalize on four break points in the fourth game of the second set, she made a visible shrugging gesture with both hands.

Naomi Osaka of Japan returns a shot to Sloane Stephens of the United States during their women’s singles match at the WTA tennis tournament in Singapore on Monday, Oct. 22, 2018. (AP Photo/Vincent Thian)

Stephens gifted the second set to Osaka when she double-faulted on a second set point in the 10th game. But Osaka appeared to be mentally fatigued and only managed to hold serve in the third game of the final set.

Sloane Stephens of the United States makes a backhand return to Naomi Osaka of Japan during their women’s singles match at the WTA tennis tournament in Singapore on Monday, Oct. 22, 2018. (AP Photo/Vincent Thian)

Stephens is now 1-0 in the Red Group, while Osaka is 0-1. Angelique Kerber and Kiki Bertens are also in the group.

Sloane Stephens of the United States reacts during a women’s singles match against Naomi Osaka of Japan at the WTA tennis tournament in Singapore on Monday, Oct. 22, 2018. (AP Photo/Vincent Thian)

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Source: The Associated Press