In 2018, when the event was still on an island instead of in an N.F.L. stadium, Federer lost in his opening round to Thanasi Kokkinakis. Though Federer had another scare in the same round this year against the qualifier Radu Albot, he rallied to win in three sets and then gathered nothing but momentum, winning five straight matches in straight sets.

“It’s easy just to say, ‘Well last year didn’t work out, so I won’t come back this year, and as I’m playing the clay, maybe add rather another clay-court event,’ ” Federer said. “But I felt like let’s extend the hardcourt season. Let’s see the new venue. To be honest, I think that was something also I was excited to see. I did feel like the game was there last year, and I thought also the game was definitely here this year even after the Australian Open. So I’m happy with the team, we took the right decision.”

The team has also agreed that Federer will play on clay for the first time since brief, unfulfilling visits to Monte Carlo and Rome in 2016. His next tournament: Madrid in early May, which will give him time to reboot and reacquaint himself with the game’s grittiest surface.

How confident is he?

“Not very confident,” he said. “I don’t even remember how to slide anymore. You know, I’m taking baby steps at this point.”

It is smart, as ever, to try to underpromise and overdeliver, particularly when you are entering the kingdom of Nadal, the 11-time French Open champion and most successful men’s clay-court player in history.

But Federer, despite his fourth-round loss to Stefanos Tsitsipas at the Australian Open, has certainly had another hardcourt run to savor in 2019.

He looked thoroughly in his element on Sunday, just as Isner feared and expected he would.

“I knew he was going to play well today; I knew he was seeing the ball very big,” Isner said. “Certainly that was the case. I wasn’t up to the task in the first set, that’s for sure.”