NEW YORK, New York -- World No.3 Naomi Osaka kicked off her US Open title defense with an impressive display of firepower, defeating the Czech Republic's Marie Bouzkova 6-4, 6-1 in the first round. 

Playing under the lights of Arthur Ashe Stadium on opening night, Osaka's powerful hardcourt game was in full flow. The two-time US Open champion fired 34 winners to 24 unforced errors to break down Bouzkova's physical defensive game and the World No.3 showed confident composure as Bouzkova ramped up the pressure in the opening set. 

Notable Stat: Osaka saved all eight break points she faced.

Turning Point: Returning well and applying defensive pressure from the baseline, Bouzkova earned an early chance to break the Osaka serve in the first set. Down 0-40 in the third game, Osaka saved all three break points to hold serve. Bouzkova did well to protect her serve until the final game of the set. In fact, until the ultimate game, Bouzkova had not missed more than three first serves in any service game.

But serving at 4-5, Bouzkova hit a pair of second serves from deuce and Osaka was able to control the rallies and earn the first break of the match. With a set in hand, Osaka raced away with the second, pocketing the match in 93 minutes to remain undefeated in the first round of a hardcourt Slam.

"I actually thought I was doing pretty well on the return games," Osaka said. "There were a couple games that were pretty close, so I just kept telling myself to keep it really tight, hopefully she'll get nervous or something. I feel like that did happen a little bit on the last set point that I was able to win.

"But, yeah, my serve's definitely one of my biggest weapons. It's able to come in when it's really necessary. But hopefully it won't be that needed in the future."

Next Up for Osaka: The No.3 seed will face Serbian qualifier Olga Danilovic in the second round on Wednesday. 

Key Quote: "Honestly, I didn't feel pressure today. I don't really know how to describe it. It may have to do with, like, my mindset change. So I didn't feel pressure today. But I think I felt nerves because I wanted to perform well. I think in my mind I told myself that if I performed well, then the outcome, even if I win or lose, should be okay. I also felt like at the end of the day you train really hard to play in front of people, especially a night match in Ashe, it's the biggest stadium in tennis. I don't know, I think that's why I felt nervous, but I definitely didn't feel any pressure."

No.2 seed Aryna Sabalenka rights the ship to beat Nina Stojanovic

Aryna Sabalenka needed three sets to defeat Serbia's Nina Stojanovic, bouncing back to win 6-4, 6-7(4), 6-0. Sabalenka extended her winning record against Stojanovic to 6-0, but the win was not as straightforward as their head-to-head would have predicted. The World No.2 stormed her way to a quick 4-1 lead in the first set, but could not dig out a hold when serving at 4-2, hitting back-to-back double-faults in the game. 

But Sabalenka quickly regained her composure and continued to pressure Stojanovic from the baseline, breaking at love for the opening set, 6-4.

The second set played out similarly to the first, except this time Stojanovic maintained her composure. Again, Sabalenka earned an early break to 4-2, but let the Serb back in the set in the very next game. The Belarusian fired three double-faults, the third on a breakpoint, to hand back the break and allow Stojanovic back on serve. Serving at 5-6, Stojanovic saved a match point with a clean backhand winner and then calmly took the tiebreak, 7-4. 

By the time the third set resumed, Sabalenka regained her focus. She hit 21 unforced errors in the second set and brought that number down to just 8 in the third to run off six straight games and seal the win after 2 hours and 24 minutes. Sabalenka finished with 43 winners to 42 unforced errors, including 13 aces and 13 double-faults.

Next up for Sabalenka: The Belarusian will face French Open semifinalist Tamara Zidansek in the second round. The Slovenian defeated Bernarda Pera, 6-4, 7-6(4).

Elise Mertens saves six match points to advance

No.15 seed Elise Mertens mounted an incredible comeback to defeat Sweden's Rebecca Peterson, saving six match points to win 3-6, 7-6(5), 7-6(5). Peterson had three match points on Mertens' serve at 3-5 in the second set, but the Belgian dug out of a 0-40 hold with the help of three aces to force Peterson to serve for the win.

Serving for the match for a second time at 6-5 in the second set, Peterson saw another pair of match points wiped out on a double-fault and a clean backhand winner from Mertens. Having come back from the brink, Mertens took the tiebreak to force a third.

This time it was Mertens who looked in control. A two-time quarterfinalist in New York, Mertens took a 3-1 lead but played a soft game at 4-3 to get broken and put Peterson back on level terms. Serving to force a decisive tiebreak, Mertens again faced down match point at 30-40, but a Peterson forehand error gave the Belgian another lifeline. 

But Mertens would need yet another comeback to seal the win. Finding her forehand range in the third-set tiebreak, Peterson built a 5-3 lead before Mertens reeled off the final four points of the match to close it out after 3 hours and 40 minutes.

Ons Jabeur steadies past Alizé Cornet

No.20 seed Ons Jabeur booked her spot in the second round with a solid performance against Chicago finalist Alizé Cornet, winning 7-5, 7-5 in 1 hour and 43 minutes. The Tunisian fired 29 winners to Cornet's 8, and was able to out-rally the indefatigable Frenchwoman in the longer rallies. In rallies lasting 5 shots or more, Jabeur nearly doubled up on Cornet, winning 35 to 18. 

Next up for Jabeur: The 20th seed will face Maria Camila Osorio Serrano in the second round. Osorio Serrano, the 2019 junior champion, won her main draw debut in dominant fashion, defeating Ivana Jorovic 6-2, 6-2.