Stefanos Tsitsipas knocked defending champion Alexander Zverev out of the Madrid Open in the quarter-finals on Friday, winning 7-5, 3-6, 6-2.
German third seed Zverev has yet to win a trophy this season and stands 4-5 on clay this spring.
Tsitsipas, the eighth seeded Greek, will face five-time champion Rafael Nadal, who blew away Swiss star Stan Wawrinka 6-1 6-2 in just one hour. The victory will be his 11th semi-final in Madrid.
In the other semi-final, Austrian Dominic Thiem will face World number one Novak Djokovic.
Thiem sensationally edged out veteran Roger Federer in three sets.
Thiem saved two match points and ended the first chapter of Roger Federer’s return to clay court tennis with a come-from-behind 3-6, 7-6 (13/11), 6-4 win.
The 37-year-old Swiss had returned this week to the surface for the first time in three years — his last clay court match was a loss to Thiem in Rome in 2016.
While Federer was heading out, there were no such problems for top seed Novak Djokovic who made the last-four when Marin Cilic withdrew and Rafael Nadal, the second seed, who brushed aside Stan Wawrinka 6-1, 6-2.
Thiem, the 2018 Roland Garros runner-up and winner of the Barcelona title last month, prevailed in two hours 10 minutes against Federer having saved two match points in a 15-minute second set tie-break.