I think she took the chances, and she played a very good match.
Yet, Osaka felt nervous against Kerber in the 23,771-seat Arthur Ashe Stadium, having lost to American Madison Keys in the third round of the U.S. Open a year ago after leading 5-1 in the third set. This time, she would not make the same mistake, in a devastating display of aggressive baseline tennis.
Not yet two full days into the U.S. Open, Arthur Ashe Stadium has already played host to a pair of major upsets.
Obviously before every first-round match I'm a little bit nervous, but especially at a grand slam and especially to defend so many points here from the final past year.
"I think, yeah, it was not my day, completely not my day today", Kerber said.
And unlike previous year, she did not take her foot off the pedal, pressing Kerber for one final break and a 6-1 victory-65 minutes in total.
Kerber's loss to Osaka also means she will slip out of the world's top 10.
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"So that helped me focus and concentrate, which I needed as Angelique gets everything back".
The world No. 6 has struggled to recapture her fine form of previous year, where she lifted two Grand Slam titles, and has failed to reach the quarter-finals of any major this season but this was as brutal an exit as you're likely to ever see.
One man certain to finish under the roof on Tuesday night was Roger Federer, whose capture of the Australian Open and Wimbledon titles in 2017 has taken his Slam count to 19.
Juan Martin del Potro, the 2009 champion in NY, starts against Switzerland's Henri Laaksonen.
Last year's runner-up and current world number one Karolina Pliskova had no trouble in her opener, as she began play on Ashe on Tuesday with a 6-2, 6-1 triumph over Poland's Magda Linette.
Federer defeated the world number 70 in straight sets in Miami this year but Tiafoe, the son of a Sierra Leone immigrant, illustrated his growing reputation by seeing off world number six Alexander Zverev in Cincinnati.
She next faces either Swedish qualifier Rebecca Peterson or Czech Denisa Allertova, with a potential fourth-round clash against French Open champion Jelena Ostapenko looming.
The Latvian won 12 of the last 14 points to seal the deal in a tie suspended at 3-1 in the final set five hours earlier.