Five sets, a tiebreak and four-plus hours later, Dominic Thiem carried his heavy legs to a victory at the 2020 U.S. Open Final at Flushing Meadows in Queens, New York.

Alexander Zverev opened the match with a convincing lead, winning the first two sets against the heavy favorite.

In the second set, however, Thiem started to improve. Fortunately for the 27-year-old Austrian, it wasn't too late. And he battled back to secure the first Grand Slam title of his career.

Thiem also became the first men's player to ever recover from a two-set deficit to win the U.S. Open Final.

The most remarkable part is how unlikely the comeback seemed. During the early stages of the match, Thiem didn't look capable of competing with Zverev.

But their fortunes reversed.

Thiem withstood the third set before Zverev began making costly mistakes. The unforced errors kept Thiem in the match and ultimately led to Zverev's downfall.

No matter the cause—fatigue, nerves or misplayed shots—Zverev failed to capitalize on his title-winning opportunity. He served for the championship but faltered with two consecutive double faults, gifting a weary Thiem new life.

Thiem took advantage of the errors and won three straight points, though Zverev recovered to force a tiebreak.

While the 2020 U.S. Open was the fourth straight major to reach a fifth set, never before had this tournament ended in a fifth-set tiebreak. Thiem made history with his triumph.

After winning the final point, Thiem collapsed to the ground in a mix of celebration and exhaustion.

"I want to congratulate Dominic on the first of many Grand Slam titles," Zverev said afterward, according to reporter Adam Zagoria. "This is not the only one."

Thiem won $3 million for the victory, while Zverev received $1.5 million for his runner-up finish.

Follow Bleacher Report writer David Kenyon on Twitter @Kenyon19_BR.