Opelka won the junior title at Wimbledon in 2015 . After he had to fend off a match point against Alex De Minaur in the first round , he subsequently defeated four seeded players u. a. the then youth world number one Taylor Fritz and defeated Mikael Ymer 7: 6, 6: 4 in the final . He was also in the final of the doubles competition that same year.
In February 2019, Opelka celebrated its first title on the ATP World Tour. In New York he defeated the Canadian qualifier Brayden Schnur in three sets in the final . In the same year he made his debut for the US Davis Cup team .
With a height of 2.11 meters (according to ATP), Opelka - together with Ivo Karlović - is the tallest player to have competed on the ATP World Tour so far, which is why he often goes with his compatriot John Isner (height: 2.08 m) is compared. One of his greatest weapons is his impact, averaging over 210 km / h. Isner and Opelka clashed three times in 2019, each time Opelka won. All ten sets went into the tie-break . At the tournament in New York he hit 43 aces in the match, Isner 38 for a new ATP record for most aces in a best-of-three match. Ultimately, Opelka also won the tournament.