Garbine Muguruza rallied from a set down to reach the second round of the US Open after Elise Mertens threatened to pull off a big upset, while Angelique Kerber had no such trouble on day one.
Muguruza came into the final major of the year with only one singles victory to her name at Flushing Meadows and the French Open champion was in danger of making a first-round exit before battling back to win 2-6 6-0 6-3.
Belgian Mertens was playing in the main draw of a grand slam singles tournament for the first time and gave a great account of herself on Louis Armstrong, but was unable to take advantage of an unconvincing display from the third seed from Spain.
Kerber spent just over half an hour on court before opponent Polona Hercog retired due to illness with the second seed in complete command leading 6-0 1-0 at Arthur Ashe Stadium, where the new roof was not required on a sunny Monday.
Last year's runner-up Roberta Vinci, who ending Serena Williams' quest to win a maiden calendar Grand Slam with a sensational semi-final victory in 2015, also coasted into the second round by ousting Anna-Lena Friedsam 6-2 6-4.
Former world number one Caroline Wozniacki came back from a set down to advance in the first contest on the new Grandstand, but there was disappointment for Coco Vandeweghe as she crashed out of her home major with a shock defeat to Naomi Osaka.
UNINSPIRING START FROM MUGURUZA
Muguruza was ousted in the second round of Wimbledon and suffered a drubbing at the hands of Monica Puig in the Rio Olympics this month before putting together a run to the semi-finals of the Western & Southern.
The world number three will have to raise her game if she is to have any chance of claiming a second grand slam victory in New York, but the manner in which she responded to losing the first set with a bagel in the second showed her strength of character.
Seven double faults and 40 unforced errors would be a concern for the powerful 22-year-old, who will come up against Anastasija Sevastova in the second round.
KERBER IN CRUISE CONTROL
While Muguruza was given a scare, Kerber barely broke sweat and was in cruise control when a struggling Hercog decided she could not continue.
The Australian Open champion and Wimbledon runner-up, who can replace Williams as the world number one at Flushing Meadows, can now prepare to take on Mirjana Lucic-Baroni.
Asked about the prospect of replacing Williams, the German said: "For sure I want to be one day number one. I think this is a goal from everybody, especially for me. But I will not putting too much pressure on myself like I said a lot of times, because I know that when I put the pressure I'm not playing my tennis."
VINCI KEEPING EXPECTATIONS IN CHECK
Vinci pulled off one of the great shocks by beating Williams in the last four last year, but the Italian knows another run to the final is a lot to ask despite making a composed start.
The experienced seventh seed, beaten by compatriot Flavia Pennetta in the final last September, refused to give Friedsam a look-in, winning 74 per cent of points on her first serve and making only 16 unforced errors to progress in 68 minutes.
"It's tough to repeat of the results of last year," she said. "But I'm number seven [seed], so of course I have a lot of pressure. They expect me to be in the semi-final or quarter-final, but I take it step by step and match by match."
WOZNIACKI MADE TO WORK, NO HOME COMFORTS FOR COCO
Wozniacki is a two-time finalist in New York and has also reached the last four twice, but the Dane has lost her way as well as being troubled by injuries and was up against it versus outsider Taylor Townsend before recovering to win 4-6 6-3 6-4.
Now ranked as low as 74th, the unseeded Wozniacki has only reached the fourth round of a major once since her appearance in the final of the US Open two years ago and faces a tough contest with world number 10 Svetlana Kuznetsova in round two.
Sloane Stephens missed her home grand slam due to injury and there was further disappointment for partisan American fans on day one when 28th seed Vandeweghe lost to Osaka of Japan in three sets.
Two-time Wimbledon champion Petra Kvitova was among the seeds to ease through, the Czech overcoming Jelena Ostapenko in straight sets.