The Spaniard also came from a set down against the 22-year-old Canadian to secure a spot in the last eight.
The German overcomes a slow start to beat the Spaniard in straight sets to setup a semifinal clash against Dominic Thiem in Madrid Open.
Both Isner and Garin needed three sets to enter the quarterfinals of the Madrid Open.
The 27-year-old is eager to get back to his best when he returns to action in Madrid Open.
Both the German and the Norwegian tennis players registered straight forward victories to enter the last-8 in Munich
Andy Murray has entered the qualifying rounds of the French Open 2021 as he targets a comeback at Wimbledon later this year.
Rafael Nadal beat compatriot Pablo Carreno Busta in the second semi-final of the Barcelona Open on Saturday to book a summit clash against Stefanos Tsitsipas.
Greek tennis star Stefanos Tsitsipas booked his place in the finals of the Barcelona Open with a convincing win over Jannik Sinner in the semi-finals.
The Spaniard, who also needed three sets in his previous round, will next play Cameron Norrie in Barcelona
King of clay courts, Rafael Nadal, had recently claimed that his rival was ‘obsessed’ with breaking records