Naomi Osaka isn’t surprised the defense of her U.S. Open title is over, as she crashed and burned under the Arthur Ashe Stadium roof on Monday. There will be no Serena Williams-Osaka final rematch.

The 13th-seeded Belinda Bencic of Switzerland continued her mastery over the Japanese-American with a 7-5, 6-4 victory in a fourth-round match. It’s the 22-year-old Bencic’s first foray into the Open quarterfinals since 2014, when she was a teenager.

She missed a lot of time in 2016 and 2017 because of wrist surgery and a stress reaction in her foot.

“It’s been a long way since then, ’’ Bencic said. “People always think I’m a little bit older than I actually am because I’ve been here since [age] 16, 17.”

Osaka, 21, came into the tournament with a left-knee injury but declined to use it as an excuse despite a second-set visit from the trainer when she was given medication. Bencic’s piercing strokes were more lethal.

Though Osaka had talked about her pattern of getting stronger as a Grand Slam wears on, she admitted this fourth-round exit was not shocking because of form, including two losses this year to Bencic.

Osaka lost in the first round at Wimbledon and third round at the French Open. She had never regained her dominance since winning the Australian Open in January for her second straight major win.

“Honestly, I’m not that mad at this,’’ Osaka said. “Until I won here last year, I was constantly a Round 3 person. Of course I can look at this and be very disappointed and mad, but I feel like: I’m not mad at it. For now, the level of tennis that I was playing in Europe was terrible — that’s kind of mean — was not that great.”

Osaka also may have suffered a letdown after her terrific and emotional victory over Coco Gauff on Saturday night in which a tear-filled post-match exchange between the two competitors lit up the internet.

“Right now I have this feeling of sadness, but I also feel like I have learned so much during this tournament,’’ Osaka said. “Of course, I wanted to defend this tournament. I feel like the steps that I have taken as a person have been much greater than I would imagine at this point.”

In the second set, Bencic posted her break at 2-2, after which Osaka took a medical timeout. A trainer came on the court and handed her a pill.

“I don’t want to say that that’s the reason that I lost, because I had played three matches before this,’’ Osaka said. “I just needed to take a painkiller.’’

She later said in Japanese it’s difficult to land hard on the leg and she limited her serve practice because of the discomfort.

Bencic ended the match by serving out at love before a quiet crowd who had tried to get Osaka going.

“I’m happy how I played and managed my nerves,’’ Bencic said. “I’m not a player who has the most winners and aces — I’m just trying to play chess.”

Both U.S. Open No. 1 seeds are gone before the quarterfinals as Novak Djokovic retired with a shoulder injury Sunday night while losing to Stan Wawrinka.

Ivan Bencic, Belinda’s father/coach who played pro hockey in the Swiss League, said the rain that forced the roof’s closure was beneficial.

“She was confident,’’ he told The Post. “When they closed the roof, that’s Belinda’s game. She can take the balls earlier.”

His daughter didn’t dispute the indoor conditions helped.

“Yeah, I wished it was going to rain, so it rained,’’ she said.

Displaying penetrating strokes, the 5-foot-9 Swiss outmaneuvered Osaka, who beat Williams in last year’s Open final in a controversial matchup.

Bencic beat Osaka twice before this year — in Madrid and at Indian Wells. She has the ability to put Osaka on the move with well-placed groundstrokes.It’s not shocking her game resembles countrywoman Martina Hingis. Melanie Hingis once served as coach.

“We didn’t try to copy Martina’s game,’’ Bencic said. “We tried to make my own game.”

At love-30 in the second set, Osaka blew an easy putaway at the net, pummeling it right at Bencic, who brilliantly batted a backhand passing shot. Osaka double-faulted at love-40 and looked despondent on the changeover, asking for the trainer.

Osaka, who has worn a left-knee sleeve after she had to retire from a match in the last Open tune-up in Cincinnati, said the difference was Bencic being more “aggressive.’’

“I didn’t move well today,’’ Osaka said. “I felt like I was always flat-footed.”

Osaka’s best memory will be on-court consoling Coco.

“I have learned over the summer that even if you aren’t playing your best, you’re going to play people who are going to play their best,’’ Osaka said. “You have to figure out how to win those matches.”