NEW YORK (AP) — Before knowing for sure that he would need to get past Jannik Sinner to reach a Grand Slam final for the first time, Felix Auger-Aliassime was asked to assess the U.S. Open's No. 1 seed and defending champion.

“What to say about Jannik’s game?” said Auger-Aliassime, who is seeded 25th. “He’s been obviously untouchable, at times.”

That's a pretty apt description for a guy closing in on becoming the first man to win consecutive titles at Flushing Meadows since Roger Federer collected five in a row from 2004 through 2008.

Jannik Sinner meets Felix Auger-Aliassime in one US Open men's semifinal.

Watch Auger-Aliassime vs. Sinner LIVE Friday, September 5 at 7 p.m. ET/ 4 p.m. PT on TSN3/5, the TSN App, and TSN.ca.

In Friday's semifinals, Auger-Aliassime might be taking on the toughest task in tennis at the moment, particularly on hard courts: Sinner is on a 26-match Grand Slam unbeaten streak on that surface, which includes titles at the past two Australian Opens in addition to last year's U.S. Open.

The 24-year-old from Italy also is coming off a Wimbledon championship in July for his fourth career major trophy.

Nothing easy about the other men's semifinal, either. That one features 24-time Slam champion Novak Djokovic, who is 38, against Carlos Alcaraz, who already owns five such titles at age 22.

“I know he’s hungry,” Alcaraz said about Djokovic, who exited each of the year's other three majors in the semifinals. “I know his ambition for more.”

Just three weeks ago, Auger-Aliassime went up against Sinner at the Cincinnati Open and it wasn't exactly a close contest. Sinner won 6-0, 6-2. They hadn't met since 2022, when Auger-Aliassime won both matchups against a guy who wasn't yet the Sinner the world knows today.

Auger-Aliassime offered a rundown of ways in which Sinner is a different player now.

“I give him credit. You have to give credit when it’s due. When somebody does the work and they improve and they get to that level, you just have to tip your hat,” said the 25-year-old from Canada, who lost his only previous Grand Slam semifinal at the 2021 U.S. Open. “Physicality, movement got much better. Stronger physically. The serve, the forehand more precise. The backhand was always consistent. The return was always good, deep. Yeah, those are the main things.”

That's all, huh?

Sinner has won his past 31 service games at the US Open

There's certainly quite a lot Sinner that does well, as he demonstrated by overwhelming his last two opponents. In a performance Sinner described as “very solid,” he dismissed No. 10 Lorenzo Musetti in the quarterfinals 6-1, 6-4, 6-2 in just 2 hours on Wednesday, two nights after an even more lopsided win, 6-1, 6-1, 6-1 against No. 23 Alexander Bublik in 1 hour, 21 minutes in the fourth round.

That's less than 3 1/2 hours combined over two matches. Auger-Aliassime needed 4 hours, 10 minutes just to get past No. 8 Alex de Minaur in his quarterfinal.

Sinner goes into Friday having claimed his past 31 service games in a row, saving 10 break points in that span.

Against Musetti, he won 42 of the 46 points — 91% — when he got his first serve in.

And then there are those crisp, clean, booming groundstrokes, including one 97 mph up-the-line forehand on a run-and-reach to earn the last break point he would need against Musetti.

“Jannik was on another level,” Musetti said. “I never played, honestly, someone who put me (in) this kind of rush in the rally.”

Alcaraz and Sinner have split the past 7 Grand Slam titles

Alcaraz and Sinner have combined to win the last seven major tournaments — while playing each other in the last two finals — and Djokovic was the champ at the other three in that stretch, including the 2023 U.S. Open.

During that same 12-Slam span, Auger-Aliassime never made it past the fourth round and exited in the first or second round at nine of them.

Not that he ever worried he wouldn't return to the latter stages again.

“If I was 35 now, maybe I would doubt if it would ever come again, like if I was losing first round (at the) back end of my career," said Auger-Aliassime, who is getting married two weeks after the U.S. Open.

“Even those last few years, I was young enough to think ... ‘OK, what do I need to improve? What’s happening? Which areas do I need to improve? What changes do I need to make?'” he said. "That’s really what I was focused about and ... the day-to-day and the process.”

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Howard Fendrich has been the AP’s tennis writer since 2002. Find his stories here: https://apnews.com/author/howard-fendrich. More AP tennis: https://apnews.com/hub/tennis