The world number two will meet Dominic Thiem in the last four in a re-match of last year’s French Open final after the Austrian overpowered Argentine Guido Pella 7-5 6-2.
Struff, ranked 51st in the world and a renowned doubles player, had impressed in Barcelona by knocking out 10th seed David Goffin and last year’s runner-up Stefanos Tsitsipas and was facing Nadal for the first time in a competitive match.
The Mallorcan broke to take a 3-1 lead with a powerful forehand winner down the line but Struff broke back to make it 4-4.
Nadal broke his opponent for a second time to avoid a tiebreak and take the set.
Neither player gave much away in a finely balanced second set, and Struff saved a break point in the eighth game to keep things finely balanced, but Nadal was saving his best tennis for the 12th game.
Nadal quickly earned three match points and seized the second with a magnificent backhand down the line to end the match in one hour and 43 minutes.
“Me and my coaches knew he (Struff) was going to play aggressively, it was one of those matches where every point counts, he put me under a lot of pressure so I had to play through that but my serve was solid throughout,” Nadal said.
“I’m aware that I was facing someone who has beaten Tsitsipas and Goffin this week so I’m very happy that I was able to win.”
Nadal won a five-set thriller against Thiem in their last meeting, in the quarter-finals of the 2018 US Open, having beaten him in straight sets in the final at Roland Garros.
Thiem won his last meeting with Nadal on Spanish soil, however, knocking the Spaniard out of last year’s Madrid Open in the quarter-finals in straight sets.
Japan’s Kei Nishikori also made it into the last four after seeing off Roberto Carballes Baena 6-4 7-5 and will face Russian Daniil Medvedev, who knocked out Chilean Nicolas Jarry 6-3 6-4.
