NEW YORK — Some players, like top-ranked Simona Halep, freely acknowledge they don't deal well with the hustle-and-bustle of the U.S. Open and all it entails.
Others, like 44th-ranked Kaia Kanepi, take to the Big Apple and its Grand Slam tournament.
Put those two types at opposite ends of a court at Flushing Meadows and watch what can happen: Halep made a quick-as-can-be exit Monday, overwhelmed by the power-based game of Kanepi 6-2, 6-4 to become the first No. 1-seeded woman to lose her opening match at the U.S. Open in the half-century of the professional era.
On a Day 1 that featured the major tournament debut of 25-second serve clocks, Halep blamed opening-round jitters, a recurring theme throughout her career. The reigning French Open champion has now lost her first match at 12 of 34 career major appearances, a stunningly high rate for such an accomplished player.
"It's always about the nerves," said Halep, who was beaten in the first round in New York by five-time major champion Maria Sharapova in 2017. "Even when you are there in the top, you feel the same nerves. You are human."
She also offered up an explanation tied to this particular site.
"Maybe the noise in the crowd. The city is busy. So everything together," said Halep, who was coming off consecutive runs to the final at hard-court tuneup tournaments at Cincinnati and Montreal. "I'm a quiet person, so maybe I like the smaller places."
Her departure means she can't stand in the way of Serena Williams, who could have faced Halep in the fourth round. Williams, the 23-time major champion who missed last year's U.S. Open because she gave birth on Sept. 1, returned with a flourish, following singer Kelly Clarkson's opening night performance in Arthur Ashe Stadium with a 6-4, 6-0 victory over Magda Linette under the lights.
"The first set was tight. It was my first back here in New York, so that wasn't the easiest," Williams told the crowd. "Once I got settled, I started doing what I'm trying to do in practice."
Williams, a six-time winner at Flushing Meadows, moved a step closer to a possible third-round matchup against her older sister, two-time winner Venus, who defeated 2004 champion Svetlana Kuznetsova 6-3, 5-7, 6-3.
Others making the second round included defending champion and No. 3 seed Sloane Stephens, two-time finalist Victoria Azarenka, and two-time major champ Garbine Muguruza.
Four seeded men lost, including No. 8 Grigor Dimitrov against three-time major champion Stan Wawrinka, who also beat him in the first round of Wimbledon, No. 16 Kyle Edmund and No. 19 Roberto Bautista Agut. Andy Murray, whose three major titles include the 2012 U.S. Open, played his first Grand Slam match in more than a year and won, eliminating James Duckworth 6-7 (5), 6-3, 7-5, 6-3.
At night, defending champion Rafael Nadal advanced when the man he beat in the 2013 French Open final, David Ferrer, stopped in the second set because of an injury, while 2009 champ Juan Martin del Potro had no trouble dismissing Donald Young 6-0, 6-3, 6-4.
Halep's loss was the first match at the rebuilt Louis Armstrong Stadium, which now has about 14,000 seats and a retractable roof, and what a way to get things started. That cover was not needed to protect from rain on Day 1 at the year's last major tournament — although some protection from the bright sun and its 90-degree (33-degree Celsius) heat might have been in order.
"The courts suit my game, and I love being in New York. I like the city," said Kanepi, who is from Estonia and is sharing a coach this week with another player, Andrea Petkovic. "I like the weather: humid and hot."
But several players had trouble in the heat, struggling with cramping or simply breathing.
Since professionals first were allowed to enter Grand Slam tournaments in 1968, only five times before Monday did women seeded No. 1 lose their opening match at a major — and never at the U.S. Open. It happened twice to Martina Hingis and once to Steffi Graf at Wimbledon, once to Angelique Kerber at the French Open and once to Virginia Ruzici at the Australian Open.
Halep got off to a slow start at Roland Garros this year, too, dropping her opening set, also by a 6-2 score, but ended up pulling out the victory there and adding six more to lift the trophy.
There would be no such turnaround for her against Kanepi, a big hitter who dictated the points to claim her second career win against a top-ranked player — but first top-20 victory since 2015. Kanepi has shown the occasional ability to grab significant results, including a run to the quarterfinals at Flushing Meadows a year ago.
On this day, Kanepi took charge of baseline exchanges, compiling a 26-9 edge in winners, 14 on her favored forehand side alone. Wearing two strips of athletic tape on her left shoulder, the right-handed Kanepi also had far more unforced errors, 28-9, but that high-risk, high-reward style ultimately paid off.
"I thought, 'I just have to be aggressive and try to stay calm,'" Kanepi said.
Early in the second set, on the way to falling behind by two breaks at 3-0, Halep slammed her racket twice, drawing a warning for a code violation from the chair umpire.
Eventually, Halep got going a bit, taking advantage of Kanepi's mistakes to break back twice and get to 4-all in that set, getting a lot of support from fans who repeatedly chanted her first name.
"I was thinking about that: Why (did) they cheer so much for her? Because normally, they cheer for the underdog," Kanepi said with a smile. "It was a bit annoying for some time, but I got over it."
Sure did. She ended a 14-stroke exchange with a cross-court forehand volley winner to break right back for a 5-4 lead, then served out the victory.