Thiem, Zverev into US Open final
Osaka, Azarenka seek third Grand Slam
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 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.
"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.
- New winner -
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.
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.
"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.
For Osaka, the fourth seed, it would be a third tennis major trophy in two years. For Azarenka, a former world number one, it would be a first since 2013.
It's a matchup between one of the game's young stars, going from strength to strength, and a veteran whose career is rejuvenated after several years in the doldrums.
The 22-year-old Osaka, her profile rapidly rising due to a combination of powerful tennis and Black Lives Matter activism, says she's better prepared than when she stunned Serena Williams in the 2018 US Open final.
"I would say I feel like my mindset is much different this time around," said Japan's Osaka, following her three-set semi-final win over American Jennifer Brady.
"I feel like I've learned so much through the ups and downs, not even counting the finals, but just regular tour tournaments.
"I would say mentally I feel stronger. I feel fitter now. It's going to be interesting to see what happens," Osaka added.
Osaka, of Japanese and Haitian heritage, is wearing different masks honoring victims of racial injustice and police brutality throughout the tournament.
The 2019 Australian Open champion has donned face coverings bearing the names of Breonna Taylor, Elijah McClain, Ahmaud Arbery, Trayvon Martin, George Floyd and Philando Castile.
She will wear another on Saturday for the Arthur Ashe showdown, which will take place without fans due to the coronavirus pandemic.
"I do think it's a very big motivating factor for me just to try to, like, get the names out to as many people as I can," Osaka said.
- 'More fun' -
The Belarusian also suffered a heartbreaking loss to Williams in the 2012 US Open, when she served for the match at 5-3 in the third set only to lose 7-5.
Azarenka's two major titles came at the Australian Open in 2012 and 2013.
She has endured a difficult few years. Injury plagued 2014 and 2015 before her career was further disrupted by a custody battle over her son, born in December 2016.
Azarenka is back up to 27th in the rankings though, and is enjoying a fairytale run at the US Open after claiming last month's Western and Southern Open tune-up event in New York.
If she defeats Osaka then she will become only the fourth women -- after Belgium's Kim Clijsters, Court and fellow Australian Evonne Goolagong -- to win Grand Slam singles titles in the Open era after having children.
Azarenka says she is benefitting from a more Zen outlook on life and revelling in the fact that few commentators expected the unseeded player to mount a challenge.
"Mentally I'm in such a different place. I think seven years ago, after I won the Australian Open... it was kind of expected for me to be in the final.
"I don't think that was the case this year. It feels more fun this year, more fulfilling, more pleasant for me."
Osaka and Azarenka have unfinished business after the Japanese pulled out of the Western & Southern final due to a hamstring injury, handing the title to Azarenka.
"She's a very, very powerful player," Azarenka said of Osaka.
"She's a great champion. She's won two already. Aren't we both looking for a third one?"