Defending champion Coco Gauff says she is treating this year's US Open as a "victory lap" after comfortably beating Varvara Gracheva in her opening match.
Gauff, 20, began her title defence with a 6-2 6-0 victory in just 66 minutes on Arthur Ashe Stadium.
The American beat Aryna Sabalenka in last year's final to win her first Grand Slam and followed that by reaching the semi-finals of the Australian Open and French Open this year.
But she has struggled for form recently, losing in the third round of the Paris Olympics before suffering early exits at tournaments in Cincinnati and Toronto.
Gauff said the past few weeks have "been a little bit tough", but she believed her performance against Gracheva was "the best tennis I have played in a while".
She added that a fan's comment on her TikTok account had helped change her perspective coming into the US Open.
"Someone commented on my TikTok saying you've won in life, literally and figuratively, and there's no point in piling pressure on yourself on a victory lap," Gauff said in her on-court interview.
"I'm just treating this tournament like that and if you defend something that means you won something."
Gauff, who fired down 10 aces, broke Gracheva's serve twice in the opening set and won the last nine games on her way to an emphatic victory.
She will face German veteran Tatjana Maria in the second round after the 37-year-old moved past Argentine qualifier Solana Sierra 6-2 6-3.
Second seed Sabalenka, one of the favourites for the title, beat Australia's Priscilla Hon 6-3 6-3 in Monday's night session on Louis Armstrong.
Zheng Qinwen reached the Australian Open final at the start of the year, losing to Aryna Sabalenka
Olympic champion Zheng Qinwen fought back from a set down to beat world number 50 Amanda Anisimova 4-6 6-4 6-2 on Louis Armstrong Stadium.
Anisimova raced out to a 5-1 first-set lead but twice failed to serve it out, before breaking Zheng for the third time to clinch the opener.
But Zheng, a little over three weeks on from her Olympic triumph in Paris, recovered well and served superbly from then on.
The Chinese seventh seed said it was the "typical match" she would have lost in the past, adding that victory was "one step forward in my mental side".
"Usually after huge success I will get a little bit too high, and until the reality slap me down again and I come back to the ground," Zheng said.
"So this time when I get a success, I'm telling myself, I don't want to let this happen. I'm really happy to get this match, because she's really tough to face."
Australian teenager Iva Jovic pulled off the biggest upset of the opening day in New York, with the 16-year-old beating world number 40 Magda Linette 6-4 6-3 for her first WTA match win.
Meanwhile, France's Clara Burel claimed an impressive comeback victory against 2017 champion Sloane Stephens.
Stephens won the first nine games of the match in 33 minutes but Burel somehow clawed her way back from a break down in both the second and third set before wrapping up a 0-6 7-5 7-5 win.
Burel will face three-time runner up Victoria Azarenka of Belarus, who beat Ukraine's Yulia Starodubtseva 3-6 6-1 6-1.
Daria Kasatkina, the 12th seed, beat Romania's Jaqueline Cristian 6-2 6-4 to progress, while Ukrainian 27th seed Elina Svitolina came through in three sets against Maria Lourdes Carle of Argentina.
Wimbledon champion Barbora Krejcikova also progressed, beating Spanish qualifier Marina Bassols Ribera 7-6 (7-3) 6-2, while American 13th seed Emma Navarro beat Anna Blinkova 6-1 6-1 in just 59 minutes.
However, Maria Sakkari became the first top-10 player to fall, with the ninth seed forced to retire injured after losing the first set to Wang Yafan.
A visibly upset Sakkari received treatment from the trainer to her shoulder and neck midway through the first set, and was ultimately unable to continue into a second.
American 14th seed Madison Keys, runner-up at Flushing Meadows in 2017, moved past Katerina Siniakova of the Czech Republic 6-4 6-1.