Top seed and world No. 1 Naomi Osaka defeated 15-year-old American Coco Gauff on Saturday in a highly anticipated third-round clash at the U.S. Open, the final major of the year.

The 21-year-old defending champion Osaka brushed aside Gauff 6-3, 6-0 at Arthur Ashe Stadium, ending the teenager's bid to reach the last 16 at back-to-back Grand Slams.

"I've watched (Gauff) play a couple of times and I've always thought she was an incredible mover, so I thought I had to get going right off the bat," Osaka said in her post-match interview.

Osaka held serve in the opening game with two aces and a pair of crisp backhand winners. She also nabbed the first break, as Gauff committed a game-ending double fault in the following game.

Gauff struggled with her serve throughout the match, but Osaka also found some difficulty as neither player managed to hold serve from the fifth through the eighth games of the set.

Osaka, who hit 24 winners in the match compared to 8 by her opponent, let a few of her misses accumulate during this stretch, and also suffered a bit of bad luck when a key shot went out after striking the top of the net.

Still up a break at 5-3, however, Osaka held serve to take a one-set advantage.

From there, the Japan native ran the table. After breaking her opponent in the first game of the second set, Osaka survived a triple-break threat in the following game.

She also relied on her powerful serve to hold at deuce in the fourth game, when her game-winning ace was called out but overturned after a challenge. Osaka had five aces in the match to two by Gauff.

The final game was a love hold for Osaka, who faces world No. 12 Belinda Bencic of Switzerland in the fourth round.

"I think this is the most focused I've been since Australia," Osaka said, referring to her second Grand Slam win in January.

Since capturing the title in Melbourne and vaulting to world No. 1, Osaka has struggled to reach tournament finals.

Osaka was considered the favorite in the pair's first match-up, but Gauff, ranked No. 140 in the world, has been the center of attention since beating Venus Williams before reaching the fourth round at Wimbledon. Osaka made a first-round exit at the grass-court tournament in London.

"It was amazing," the teen star said about the experience of facing Osaka in New York. "She did amazing and I'm going to learn a lot from this match."

The match between the two young stars attracted attention among fellow tennis players and fans even before it started.

Serena Williams, a 23-time Grand Slam champion and last year's runner-up at the U.S. Open, said Friday she was looking forward to the match.