Daniil Medvedev rallied from a set down to beat world No 1 Novak Djokovic and reach the Western & Southern Open final, where he will face David Goffin.
Despite losing the first set, the Russian rallied from break point and 3-4 down in the second set to produce some blistering serving and huge winners to inflict a rare semi-final defeat on Djokovic.
The Serb, whose only Masters title this year came in Madrid, was beaten in one hour and 43 minutes for a first Masters semi-final defeat after winning the opening set in six years.
Medvedev, who will rise to at least seventh in the world rankings on Monday, is at the high point of a spectacular run of form that has seen him reach a third consecutive final.
The Russian has lost just two of his last 15 matches, but both of those defeats have been finals, losing to Nick Kyrgios in Washington at the start of the month before suffering defeat against Rafael Nadal in the Montreal final last Sunday.
Before this year he had never been beyond the third round of a Masters event, but Medvedev, who also beat Djokovic in Monte Carlo, has reached at least the last four in three of the last four 1000 Series tournaments.
He will start as favourite against Belgium's resurgent Goffin, who has returning to winning ways with a spectacular run in Cincinnati.
In the earlier semi-final, the 28-year-old beat Andy Murray's conqueror Richard Gasquet 6-3 6-4 to also reach his first ATP Masters 1000 final.
World No 19 Goffin, who beat Medvedev in the third round at Wimbledon earlier this year, is chasing a first title since 2017 and stands on the brink of the biggest title of his career having won his first Masters semi-final in five attempts.
In the women's final, Svetlana Kuznetsova will meet Madison Keys after the Russian's remarkable run in Ohio continued with a straight-sets win over Ashleigh Barty.
Barty, who could have returned to world No 1 had she reached the final, lost 6-2 6-4 to the 34-year-old Russian.
Kuznetsova, US Open champion in 2004 and French Open champion in 2009, has slipped to world no 153 as a result of injuries but having accepted a wild card has beaten Sloane Stephens, Czech third seed Karolina Pliskova and Barty in successive matches to reach the final.
Keys won the battle of the Americans against Sofia Kenin running out a 7-5 6-4 winner in their semi-final.