Roger Federer raised some eyebrows when he said on the Arthur Ashe Stadium court Tuesday night after his first-round trouncing of Japan’s Yoshiito Nishioka, “[It’s] almost time to retire, but not yet.’’

Huh? Federer, at age 37, clarified the remark later. He’s committed to the 2019 Laver Cup in Geneva in late September, so who knows if that event in his home country will be his swan song.

Federer’s elegant strokes were on full display against the overmatched Nishioka despite a drop in focus late in the third set as he moved to 18-0 in first-rounders at the Open and 35-2 in night-card Ashe Stadium matches with a 6-2, 6-2, 6-4 win.

Asked about the R-word, Federer said, “That was meaning like I never lost a first-round match here at the Open. You don’t want that to happen next year. I said maybe I could retire now because I protected my 18 first-run wins. It’s a total joke, yes. Please don’t read into it.’’

Tennis legend Rod Laver said last week Federer desperately needs a few three-set cruisers the opening week to have enough left in the tank at the end. And it’s especially true in this unbearable heat wave when the temperature was still at 95 degrees when Federer took the court at 7:30 p.m.

Federer was sweating profusely during his post-match interview on the court. He could get Aussie bad boy Nick Kyrgios in Round 3 — a dangerous foe. Federer said Kyrgios behaves himself when they play but admitted he’s getting worse in other matches when he seems to stop trying.

Federer wore all maroon, marooning his poor opponent, the 22-year-old lefty Nishioka who once was a top-50 player before knee surgery.

Federer toyed with his Japanese opponent for most of the match with some of his trickier drop shots and crazy angles. But at 5-1 in the third set, Federer got too cocky and Nishioka won three straight games, shaking his fist to the crowd to pump it up.

Federer said the Open hard courts are playing slower than ever, making him almost feel like he’s at a clay court event. He looked shaky in Cincinnati where he had complained about the tennis balls being too lively.

“This seems the slowest U.S. Open we’ve seen in years,’’ Federer said.

At Federer’s age, that may be what the doctor ordered.