Cincinnati, USA: World number one Novak Djokovic wilted under pressure from Daniil Medvedev on Saturday, falling 3-6, 6-3, 6-3 to the ninth-seeded Russian in the Cincinnati Masters semi-finals.
Medvedev's upset win sent him into a title showdown with another unexpected finalist, 16th-seeded Belgian David Goffin, who defeated France's Richard Gasquet 6-3, 6-4 to reach his first ATP Masters 1000 final.
A fuming Djokovic, who looked to have control of the contest in the early going, was caught out when Medvedev stepped things up in the second set.
"I don't know how I turned it around, I was so tired after the first set and I thought I might not be able to keep up the intensity," said Medvedev, who has competed in 15 hardcourt matches since July 30.
"But I had a momentum chance in the second set and the crowd gave me energy," added the Russian, who will be playing his second Masters series final in eight days, after falling to Rafael Nadal in Montreal last Sunday.
"Novak had been destroying me on second serve, so I just went for it," Medvedev said. "It's a great feeling to win and beat the number one."
Djokovic, the defending champion who was playing his first tournament since his Wimbledon triumph in July, need some time to cool down before pondering his loss.
"He deserves to be in the mix, certainly, with all his results," Djokovic said. "He's working his way to top 5. "He's definitely one of the best players in the world at this moment."
Djokovic said there was little he could do in the face of Medvedev's go-for-broke style.
"When I had my racquet on the ball I was returning also his serves, but you can't really predict someone or prepare yourself for someone serving that big second serve consistently from 4-3 to the end of the match with making maybe two double faults out of God knows how many serves," he said.
With the US Open starting on August 26, Djokovic said he took "mostly positives" from the week.
"Today I did lose a tennis match, but I didn't do too much wrong," he said. "So I'll take that and I'll move forward to New York and have a good practice week.
"I'm going to go to fight for a title as everyone else does -- and I like my chances."
Medvedev won 12 of the last 14 points in the second set to square the match against Djokovic, then ran up a 3-1 lead in the third on the way to victory on his first match point.
There was an upset in the women's draw as well, as Russian veteran Svetlana Kuznetsova defeated top-seeded Australian Ashleigh Barty 6-2, 6-4.
Kuznetsova, a two-time Grand Slam champion who has been hindered lately by injury, will be in search of her 19th WTA title -- and her first in more than a year -- when she takes on American Madison Keys in the final. Keys, the 2017 US Open runner-up, defeated compatriot Sofia Kenin 7-5, 6-4.
Kuznetsova denied Barty a chance to reclaim the world number one ranking, which the Australian would have done by reaching the final.
Instead the triumph by 34-year-old Kuznetsova leaves injured Naomi Osaka atop the rankings with the US Open looming.
Barty, who had rallied from a set down in each of her previous two matches, also said she was taking positives from the week to Flushing Meadows.
"This was a week that I battled through," Barty said. "At times I played some good stuff. At times I played some pretty awful stuff.
"I've learned a lot from this week, and there are nothing but positives going into New York," she said.
Keys booked her finals spot as she won an all-American match littered with 12 breaks of serve.
She earned match points with a flick volley winner angled steeply cross-court and amazed herself with the get. "I looked at my box in shock," she admitted. "I'm really feeling great about my tennis.