Holger Rune stunned home favourite Carlos Alcaraz to win the Barcelona Open.

Spaniard Alcaraz had hoped to claim a third title in Catalonia and second in a row after winning in Monte Carlo last weekend, but he needed treatment for an apparent groin problem in the second set and fell to a 7-6 (6) 6-2 defeat.

With Alexander Zverev celebrating his 28th birthday by winning the BMW Open on home soil in Munich, Alcaraz will drop back to third in the world rankings behind the German on Monday.

Alcaraz began strongly and broke serve in the fifth game but fellow 21-year-old Rune hit straight back and from there was the better player, finally taking his fifth set point in the tie-break.

Alcaraz applied pressure early in the second set but Rune withstood it, and it became clear all was not well with the Spaniard when he headed off court for a medical time-out.

His final chance came and went with two break points in the sixth game before Rune celebrated his fifth ATP Tour title and a return to the top 10.

“It means the world,” the Dane said on Sky Sports. “It was such a great match. In the beginning I was a bit stressed because Carlos obviously played big-time tennis. I had to breathe a lot and find my rhythm.

“Then it was a big battle in the first set, the first set was extremely important. I’m so proud of myself.”

Rune revealed he thought back to Alcaraz’s defeat by Novak Djokovic in the Olympic final last summer as he sought a winning strategy.

“I kind of played it in my mind,” he said. “I thought to myself, ‘OK, let’s try to play that kind of style, really make him play a lot of balls’. I’m very happy how I stayed composed when it really mattered, and I was also very brave.”

Earlier, Zverev won his third title in Munich in comprehensive fashion with a 6-2 6-4 victory over second seed Ben Shelton.

The German had struggled since reaching his third grand slam final at the Australian Open in January, and he said: “It’s extremely special, I always love winning tournaments in Germany. It’s definitely a great birthday present.”