Danish teenager Holger Rune has won his first title on the ATP Tour after his Dutch opponent Botic van de Zandschulp retired injured during the first set of their final in the Munich clay-court event.

The rising 19-year-old had upset top-seeded Olympic champion Alexander Zverev in the second round en route to Sunday’s unexpected triumph.

He quickly trailed 4-1 in the first ATP final for both players but then won the next two games before van de Zandschulp called for the tournament doctor.

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He received treatment and left the court for several minutes with what appeared to be chest problems, and retired after playing just four more points.

The 70th-ranked Rune has become the second youngest champion in Munich after Guillermo Perez-Roldan, who won it at age 17 in 1987 and successfully defended his title a year later.

The youngster could hardly believe his extraordinary week’s work after having not won consecutive tour-level matches in 2022 prior to the tournament.

He also defeated home favourite Oscar Otte 6-4 6-4 in both players’ first ATP Tour semi-final on Saturday.

Rune, who also celebrated his 19th birthday on Friday two days after he stunned Zverev, also ousted Jiri Lehecka and Emil Ruusuvuori on the way to his maiden final.