Novak Djokovic acknowledged he had rarely faced the sort of barrage a resilient Daniil Medvedev used so effectively to shock the World No 1 3-6, 6-3, 6-3 in the Cincinnati Masters semi-finals on Saturday.
After losing the first set, Medvedev changed his approach midway through the second set, the Russian going for broke with pretty much every shot, particularly on second serve.
The complexion of the match changed in a heartbeat as Medvedev overpowered the previously dominant Djokovic.
"I did not experience this too many times in my career that someone goes so big on second serves and just serves two first serves basically for an extended period of time," the vanquished Serbian told reporters.
"When someone serves a 128 miles-per-hour second serve and doesn't make too many doubles faults and goes for every shot, you just have to put your hat down and congratulate him."
Medvedev explained why he had switched tactics.
"I was so tired in the first set and playing Novak, I thought I'm not going to be able to keep the intensity," the world number eight said in a courtside interview with ESPN.
"Then there was one momentum change in the second and I just started playing unbelievable."
Medvedev added that it was par for the course to go for broke on his second serve when trailing in a match.
"I do it all the time when my second serve doesn't work. Novak, he was destroying me on the second serve so at one moment, at three-all, love-30, I'm like 'okay, what's the matter.'"
He reeled off four successive points, including an ace on second serve, to hold and then broke Djokovic in the next game by ripping a winner down the line to seize the initiative.
Medvedev, who also beat Djokovic in April at Monte Carlo, will play Belgian David Goffin in the final on Sunday.
It will be the third successive final for 23-year-old Medvedev, who lost to Nick Kyrgios in Washington and Rafael Nadal in Montreal.
Djokovic, meanwhile, will regroup for the US Open starting on Monday week, and he did not sound particularly concerned by his latest defeat, preferring instead to heap praise on his opponent.
"He played amazing tennis from 4-3 in the second set. Not much that I could really do.
"He's working his way to the top five (in the world). Today I did lose a tennis match, but I didn't do too much wrong."
The 16th seeded Goffin beat France's Richard Gasquet 6-3, 6-4 in the other semi-final.
"I'm really happy," said Goffin.
"I've played the best tennis here in the past few years... It's a great moment for me."
A quick break saw Goffin surge to a 4-1 lead with a backhand winner down the line in the first set.
Gasquet grabbed a 2-0 lead in the second set before Goffin claimed five of the next six games.
He won the set and the match when a Gasquet backhand was long.
Goffin had received a walkover into the semi-finals after Yoshihito Nishioka was forced to withdraw due to food poisoning.
"It was almost a day off, so I was fresh and physically 100 percent today to play against Richard," the Belgian said.
Goffin added that he was "lost" after the walkover.
"I didn't know what to do. Do I have another practice session, go to the physio and have some treatment? I didn't know," the Belgian said.
"I decided to go on the court for some practice and do what I normally do after."
