Madrid (EFE) ), by 4-6, 6-3 and 6-4.
Previously, Alcaraz had beaten Croatian Borna Coric (20) 6-4, 6-3.
33-year-old Struff will play the final of a category 1,000 tournament for the first time in his career, while for Alcaraz it will be the fourth, with victories in the previous three: Miami and Madrid 2022 and Indian Wells 2023.
The German player endured a highly physically demanding semifinal, unlike Karatsev, who already came out to play with a bandage on his left thigh and had to be treated by the physiotherapist in the third set.
Alcaraz has played with the German, twice, in two Grand Slams, with a victory for each: Struff’s in the round of 32 at Roland Garros in 2021, Alcaraz’s in the first round of Wimbledon in 2022, in five sleeves.
In the previous phase in Madrid, ten days ago, Karatsev had defeated Struff 6-4, 6-2, on the modest track 8 of the Caja Mágica.
The German was benefited by a casualty and was re-fished for the main draw, where as a ‘lucky loser’ he became great until reaching the final, the most important of his life.