Britain's Toby Samuel won his maiden Grand Slam match after an impressive straight-sets victory while Katie Boulter also won through, but Cameron Norrie lost on the opening day of the US Open.
Samuel, who came through three rounds of qualifying, stunned former top 20 player Tomas Machac 6-2 6-3 6-2 in just 90 minutes with a superb display of serving and groundstroke hitting.
The win means Samuel will move into the top 100 on the ATP rankings and he will play 18th seed Jiri Lehecka, another Czech player, in the next round on Wednesday
"I'm so tired - but otherwise I'm so happy to have got the job done there," said Samuel, who was ranked 683 in the world this time last year.
"I played a great match - I'm just so thankful to everyone that has supported me to this moment, and hopefully I can carry on into next week.
"The first two sets I wasn't missing any balls. In the third, he came out a bit stronger - I had a little dip in the first few games, but I came out of it quickly. I'm just going to try and do exactly what I did today in the next match."
Samuel was a clear step above Machac for most of the match with early breaks in the first and second set enough to take a quick two sets lead.
The 23-year-old barely made any unforced errors and was not threatened on serve until the start of the third set, when he was broken, but he won six consecutive games to break his winless Grand Slam duck.
In the women's draw Katie Boulter came through a tough match against American wild card Carol Young Suh Lee.
British number one Boulter, 30, looked to be cruising through at a set and a break ahead, only for some costly double-faults to let Lee back in.
However Boulter, cheered on by new husband Alex De Minaur, gathered herself on a noisy, partisan Court Five to win 6-4 3-6 6-0.
A tricky assignment could await in round two, however, with a potential tie against this year's Wimbledon runner-up Karolina Muchova.
Norrie was unable to join Samuel in the second round after a third successive first-round exit at Grand Slams this year as he lost 7-6 (8-6) 2-6 2-6 3-6 to France's Luca Van Assche.
A topsy-turvy opening set went Norris' way but his performance suddenly dipped early in the second set and he was never able to recover as Van Assche gained confidence in the long baseline rallies.
Norrie, who has been overtaken as British No 1 by Arthur Fery after his run to the Winston-Salem final on Saturday, became increasingly frustrated but showed some fight after being broken early in the fourth set.
He got back to 3-3 with some superb hitting but Van Assche resisted the late rally to break again and book a spot in the second round of the US Open for the first time in his career.
"It was really tough," said Norrie. "I was pretty nervous and it showed in the beginning of the first set, and I did well to steal that first set.
"But I could never really maintain a good level of energy and momentum, and I'd play well for a little bit and then drop off a couple of games here and there.
"So that was super frustrating and pretty surprising. I felt like I lost to myself today."
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