Madison Keys’ dominant first set was undone by a couple of heartbreaking tiebreakers.

And when it was over, so was the hope of an all-American U.S. Open final.

While Keys landed the first punch, Aryna Sabalenka showed she had a chin.

She got up off the mat with an 0-6, 7-6 (1), 7-6 (5) come-from-behind semifinal victory at Arthur Ashe Stadium.

After a staggeringly easy first set when Keys dropped the second in a 7-1 tiebreaker, many expected the consistent Sabalenka to take control.

The big Belarusian had won the Australian Open and reached the semis at both the French Open and Wimbledon, boasting a stronger pedigree and better season.

It was a gutty performance from the second-seeded Sabalenka, who had her first legitimate test in Flushing Meadows and will take over the World No. 1 ranking on Monday.

Now, the only question is whether she’ll do it as U.S. Open champion, facing American Coco Gauff in the final.

Keys put Sabalenka on the back foot at times.

She’d suffered an authoritative quarterfinal loss at Wimbledon, Sabalenka breezing to a 6-2, 6-4 victory.

But Thursday night Keys turned the tables, frustrating her foe.

After a big break by Keys, Sabalenka walked toward her box and smashed her racket, and then she tossed it up at her box.

It didn’t make it that far, falling back to the ground as Sabalenka stalked off and left it there.

But she eventually got her mind right.