Naomi Osaka put her right hand in the shape of a gun and pointed two fingers at her temple, her face grim, while she looked toward her guest box. Babos got 62 percent of her first serves in play and saved three of her four break points while hitting seven aces.
Greek eighth seed Tsitsipas struggled with cramps and accused umpires of having "preferences" after he slumped to a 6-4, 6-7 (5/7), 7-6 (9/7), 7-5 defeat by Next Gen rival Andrey Rublev in a gruelling four-hour slog.
"I was trying to calm myself down", Gauff said in her post-match interview.
It was the first career meeting between Andreescu and the 33-year-old Flipkens, a former world No. 13 who came into the tournament ranked 110th. "That's the most important part if you want to win", said Petkovic, who next faces Belgian 25th seed Elise Mertens.
Nadal never trailed in the first set, but trailed Millman twice in the second set.
Andrea Petkovic started the day at the U.S. Open with an upset, beating No. 6 seed Petra Kvitova 6-4, 6-4. Bryant, the retired National Basketball Association superstar, came to the U.S. Open to promote a new book "Legacy and the Queen" that he conceived and that Osaka has supported.
Osaka's victory sets up the possibility of an intriguing next match.
"I could kind of see how stressed out (Kerber) was and that was in my favor", Osaka said.
"I think I gave them a heart attack, especially my mom", Gauff said.
Nadal is now 15-0 in first round matches at the U.S Open.
Although she's only 21, Naomi Osaka has already acquired two Grand Slam singles titles and acute powers of observation.
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The number-one ranked Japanese beat her Russian opponent 6-4 6-7 6-2 to book her berth in the next round.
"I'm really grateful they came out", Osaka said. I went on court today against a tough opponent knowing that I needed to play well to win.
Coco Gauff is quickly becoming the Comeback Kid.
Gauff, 15, overcame fellow teenager Anastasia Potapova 3-6 6-2 6-4 at Louis Armstrong Stadium on Tuesday. "I was nearly out".
Elsewhere, Wimbledon champion Simona Halep scuppered lucky loser Nicole Gibbs, while 19 year-old Canadian sensation Bianca Andreescu, who captured the Rogers Cup title at home in Toronto earlier this month, eased past 17 year-old Katie Volynets 6-2 6-4.
All along the way, her mother and father were clapping and yelling, celebrating almost every point their daughter claimed.
Earlier, two top-10 men considered possible future major champs tumbled to first-round exits for the second straight Slam: No. 4 Dominic Thiem and No. 8 Stefanos Tsitsipas.
"I don't know how the ending is going to be". Soon after that she parted with her coach, Sascha Bajin, and later flailed a bit, losing in the first round at Wimbledon and the third round at the French Open.
Millman delivered the upset of the tournament past year when he beat five-time victor Roger Federer in a surprising run to the quarter-finals but he was unable to recreate the same magic against the relentless Spanish second seed.
The No. 1 seed gave them plenty to cheer along the way, especially the forehand victor on break point that gave her a 4-3 lead in the second set after Linette had grabbed the first three games.