But Nadal again lost his serve. As Thiem took a 4-3 lead, the stadium’s audio and visual systems stopped working, turning the giant screens blank and leaving the umpire unable to announce the score over the loudspeakers.
By this stage, though, Thiem did not need anybody telling him that he was on his way to a major upset victory. With the partisan crowd also turning more silent, he won his next service game at love, hitting three missile forehands that landed as if guided toward the same corner spot, well out of reach of Nadal as he scrambled across the baseline.
With a fabulous backhand winner down the line, Thiem reached his first match point at 3-5. But Nadal served his way out of trouble. Thiem then converted his second opportunity, ending Nadal’s incredible run on clay and winning the match in just under two hours.
In the semifinals on Saturday, Thiem will face Kevin Anderson, the South African who was a finalist at the last United States Open. In the other men’s semifinal, Alexander Zverev will play Denis Shapovalov.
After the match, Thiem said that his make-or-break approach to playing Nadal had paid off.
“If I just played like I would normally, you have no chance,” Thiem said. “It has to be a special day — the shots have to work — and that was the case today.”
Nadal had beaten Thiem, 6-0, 6-2, in the quarterfinals of the Monte Carlo Masters three weeks ago.
“He was better than me today,” Nadal said. “That’s the end of the story.”
Nadal said that he “didn’t read the ball good enough” and struggled with Thiem’s heavy topspin shots in the high-altitude conditions in Madrid, compared with seaside Monte Carlo and Barcelona, his most recent tournament wins.