– When Roger Federer won his 19th grand slam title earlier this year at Wimbledon, he did it without dropping a set along the way.

His opening round match in Arthur Ashe Stadium was a different affair as he struggled to beat 19-year-old American Frances Tiafoe 4-6, 6-2, 6-1, 1-6, 6-4.

"I had a bit of a slow start today, but Frances also felt good from the beginning. I was maybe a bit worried at the beginning with my back issue from a couple of weeks ago," Federer acknowledged, "but was eventually able to let go."

Tiafoe took the first set but Federer was able to swing the momentum back quickly, grabbing the next two sets and it looked as if he would breeze into the second round after a slow start.

Tiafoe responded, dominating the fourth set and setting up a decisive fifth. Federer took control of the fifth set early, grabbing a break for a 3-1 lead. He had the chance to serve out for the win, leading 5-3, but Tiafoe broke back.

But Federer, the five-time U.S. Open champion, showed why he's won more majors than any man to play the game as he broke Tiafoe and ended the drama.

Reigning champ Kerber, falls

The question was rather simple after Angelique Kerber became only the second defending U.S. Open champion in the professional era to lose in the first round.

The surprisingly lopsided 6-3, 6-1 loss to 45th-ranked Naomi Osaka of Japan under the closed roof in Arthur Ashe Stadium at a rainy Flushing Meadows on Tuesday was former No. 1 Kerber's latest in a long list of disappointing performances in 2017, so she was asked what she thinks went wrong this season.

She sighed, shrugged her shoulders and began to answer: "I don't know."

Showers showed up before noon Tuesday and led to the postponements of dozens of matches. The only court used in the afternoon and evening was Ashe, thanks to the retractable cover.

Karolina Pliskova, who is seeded No. 1, easily advanced by beating Magda Linette 6-2, 6-1, French Open champion Jelena Ostapenko got past Lara Arruabarrena 6-2, 1-6, 6-1 in a match that started on Court 17 then was moved indoors at Ashe. No. 15 Madison Keys moved into the second round by beating Elise Mertens 6-3, 7-6 (6).

No. 1 men's seed Rafael Nadal overcame a first-set hiccup before overpowering Dusan Lajovic 7-6 (6), 6-2, 6-2.