Struff defeated fourth-seeded Stefanos Tsitsipas 7-6 (5), 5-7, 6-3 on Thursday to earn a rematch with Karatsev in the quarterfinals.
Jan-Lennard Struff thought he was out of the Madrid Open after losing in the final round of qualifying against Aslan Karatsev last week.
Then, as the tournament's so-called lucky loser, he received an unexpected spot in the main draw and has really made it count, defeating fourth-seeded Stefanos Tsitsipas 7-6 (5), 5-7, 6-3 on Thursday to set up another shot at Karatsev—this time in the semifinals.
The big-serving German is only the third lucky loser to reach the Masters 1000 semifinals.
Women's No. 1 Iga Swiatek and No. 2 Aryna Sabalenka have advanced to the finals and will face off for the title on Saturday. It will be a rematch of the final from two weeks ago in Stuttgart, which Swiatek won. It will be the first time since No. 1 that the top two ranked players clash in a WTA 1000 final. Serena Williams won the 2014 Miami Open over second-ranked Li Na.
"I really want this revenge," Sabalenka stated.
Stuff, 33, has a chance to avenge a 6-4, 6-2 qualifying loss to Karatsev. He only got into the main draw when another player dropped out.
Struff had only dropped five service games in the main draw en route to the quarterfinals, and only one against Tsitsipas on his road to triumph in Madrid.
"It feels incredible. Struff described the battle as "extremely difficult." "I'm overjoyed that I played so well today."
Tsitsipas, rated fifth, was coming off a final appearance at the Barcelona Open, where he was defeated by Carlos Alcaraz. In 2019, he finished second to Novak Djokovic in Madrid.
In the other semifinal, defending champion Alcaraz will meet 17th-seeded Borna Coric.
Karatsev advanced to his first Masters 1000 semifinal by defeating Chinese player Zhang Zhizhen 7-6 (3), 6-4.
In the first set, the veteran Russian saved all three break points he faced and converted his only opportunity in the second.
"Aslan has been playing fantastic this week, and he beat me pretty easily in qualifiers," Struff remarked. "I didn't play my best tennis in that match, but he forced me to play poorly." I believe we should evaluate it now, focus on the match tomorrow, and I hope to do better."
Karatsev has reached the 14th position. In 2021, he became the first man to reach the Australian Open semifinals on his Grand Slam debut.
He became only the second qualifier to reach the Madrid semifinals.
"I started the year inside the top 100, but then I dropped and lost some matches," he explained. "You have to keep going and believe, and I have a team behind me that is always supporting and believing in me."
Swiatek defeated 12th-seeded Veronika Kudermetova 6-1, 6-1 to reach her first Madrid final and set up a rematch with Sabalenka, who defeated Maria Sakkari 6-4, 6-1.
Swiatek has improved to 27-1 on clay since the beginning of the season. She will compete in her seventh WTA 1000 final of her career, tying Caroline Wozniacki for the most final appearances at this level before turning 22 since the WTA 1000 competitions began in 2009.
"I'm just happy that I have a chance to be in the final," Swiatek remarked.
Sabalenka, the 2021 Madrid winner, led 3-0 until the ninth-seeded Sakkari broke back. She then won nine of the next eleven games, including the final five, to easily win the series.
"It was actually my best match of the tournament," Sabalenka said of her victory. "I'm very pleased with my performance, particularly my mental game."
The Australian Open winner is attempting to win her fifth WTA 1000 title and 13th career title.
It will be only the third time in the last 40 years that the top two women's tennis players meet twice on clay in the same season.
Struff Upsets Tsitsipas To Set Up Semifinal Rematch With Karatsev At Madrid Open