World No.3 Naomi Osaka of Japan kicked off her US Open title defence with an impressive win over Czech Republic's Marie Bouzkova 6-4, 6-1 in the first round under lights at the Arthur Ashe Stadium late on Monday night.
The two-time US Open champion fired 34 winners to 24 unforced errors to break down Bouzkova's defensive game in the first set and then ramped up the pressure to win the second set with ease.
The No.3 seed will face Serbian qualifier Olga Danilovic in the second round on Wednesday.
Aryna Sabalenka of Belarus 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 hold serve at 4-2, hitting back-to-back double-faults in the game.
But the Belarusian quickly regained her composure and continued to pressure Stojanovic from the baseline, breaking at love for the opening set, 6-4.
Sabalenka will face French Open semifinalist Tamara Zidansek in the second round. The Slovenian defeated Bernarda Pera of the US, 6-4, 7-6(4).
No.15 seed Elise Mertens of Belgium made an incredible comeback to defeat Sweden's Rebecca Peterson, saving six match points to win 3-6, 7-6(5), 7-6(5).
Meanwhile no.20 seed Ons Jabeur booked her spot in the second round with a solid performance against Chicago finalist Alize Cornet, winning 7-5, 7-5 in 1 hour and 43 minutes. The Tunisian fired 29 winners to Cornet's eight, and was able to out-rally the indefatigable Frenchwoman in the longer rallies. In rallies lasting five shots or more, Jabeur nearly doubled up on Cornet, winning 35 to 18.
The 20th seed Jabeur will face Maria Camila Osorio Serrano of Colombia in the second round. Osorio Serrano, the 2019 junior champion, won her main draw debut in dominant fashion, defeating Ivana Jorovic of Serbia 6-2, 6-2.