Dominic Thiem of Austria will play Germany's Alexander Zverev in the US Open final for their first Grand Slam titles after they won their last-four matches in contrasting styles Friday.

Second seed Thiem ousted third-seeded Russian and last year's runner-up Daniil Medvedev in a closely fought three-setter that was packed with powerful baseline rallies and impressive serving.

The 27-year-old Thiem won 6-2, 7-6 (9/7) 7-6 (7/5) in 2hr 56 min inside Arthur Ashe Stadium to reach his fourth Grand Slam final.

Earlier, Zverev came from two sets down to complete a remarkable comeback against 20th-seeded Spaniard Pablo Carreno Busta and reach his first tennis major final.

The 23-year-old German won an error-strewn, scrappy encounter 2-6, 6-3, 6-4, 6-3 in 3hr 23min, also on the famous Ashe court.

It marked the first time in Zverev's career that he came from two sets behind to win.

Dominic Thiem of Austria returns the ball during his semi-final against Daniil Medvedev of Russia at the 2020 US Open
Dominic Thiem of Austria returns the ball during his semi-final against Daniil Medvedev of Russia at the 2020 US Open GETTY IMAGES NORTH AMERICA / MATTHEW STOCKMAN

"I actually looked at the scoreboard when I was down two sets to love," Zverev said.

"I was like, 'I can't believe it. I'm playing in a semi-final, I'm supposed to be the favourite and I have no chance, I'm playing that bad."

Zverev made 36 unforced errors in the first two sets compared to just 12 for Carreno Busta as the nerves of the occasion seemed to get the better of him.

But Zverev began to cut down on his mistakes in the third set, upping his service game and taking control of rallies with more powerful, accurate groundstrokes.

"I started taking the ball more on the rise. I started giving myself the chance to be the one that is aggressive," said the German, adding: "I'm through to my first Grand Slam final and that's all that matters."

Carreno Busta said he had lost "a big opportunity" to reach a first Slam final.

"I made the semi-finals here. I know that is a good result, is a good performance, but now in this moment it's tough," he told reporters.

Alexander Zverev of Germany celebrates winning his semi-final match against Pablo Carreno Busta of Spain at the 2020 US Open
Alexander Zverev of Germany celebrates winning his semi-final match against Pablo Carreno Busta of Spain at the 2020 US Open GETTY IMAGES NORTH AMERICA / MATTHEW STOCKMAN

Zverev becomes the first German man to reach the final of a tennis major since Rainer Schuttler at the 2003 Australian Open.

This year's US Open field has been depleted by the absence of Roger Federer and Rafael Nadal.

The tournament was blown wide open by the disqualification of world number one and heavy favourite Novak Djokovic in the last 16 for hitting a line judge with the ball.

It means Sunday's final will see a first-time Grand Slam champion for the first time since Croatian Marin Cilic won at Flushing Meadows in 2014.

It also means there will be a Grand Slam champion other than Djokovic, Nadal or Federer for the first time since Switzerland's Stan Wawrinka won the third of his tennis majors at the US Open in 2016.

Thiem, ranked third in the world, will be playing his second consecutive Slam final after reaching the last-two at this year's Australian Open.

He also lost in the French Open final in 2018 and 2019.

Thiem's semi-final score slightly flattered him. It was a high-quality affair that saw small shifts in momentum in both players' direction at different stages.

Ultimately the match was decided by Thiem winning points at key moments, with Medvedev squandering a 4-2 lead in the second.

He was also on set point while serving at 5-3 in the third set but Thiem won a 38-shot rally to take the game and bring the set back on serve before clinching the tie-break and the match.

"It was great tennis from both of us," said Thiem, whose attention now turns to Zverev.

"We have such a great friendship and rivalry. It's really amazing thing that we will face off against each other in a Slam final," he added.