Reilly Opelka defeats John Isner in four sets at the Australian Open on Monday.

Reilly Opelka is the champion in Champaign, surging into the Top 100 of the ATP Rankings.

Reilly Opelka claims his second ATP Challenger Tour title of the year, prevailing in Knoxville.

Reilly Opelka throws out the first pitch at the Chicago White Sox game, during the Oracle Challenger Series Chicago.

Reilly Opelka throws out the first pitch at the Chicago White Sox game.

Reilly Opelka throws out the first pitch at the Chicago White Sox game.

Reilly Opelka is looking to make his second Grand Slam appearance in Paris.

Thumbs up from Reilly Opelka, who triumphed in Bordeaux for his first clay-court crown.

Reilly Opelka reigns in Bordeaux, claiming his first clay-court title.

Reilly Opelka kicks off his clay-court campaign with a semi-final appearance at the Sarasota Open.

From left to right: #NextGenATP players Andrey Rublev, Taylor Fritz, Alex de Minaur, Stefanos Tsitsipas and Reilly Opelka participate in a question-and-answer session on Tuesday in Indian Wells.

Reilly Opelka pulls off the biggest win of his career against Jack Sock at the Delray Beach Open on Wednesday.

#NextGenATP Americans Reilly Opelka and Taylor Fritz assist at the tournament draw and participate in a Q&A during a charity fundraiser for the YMCA.

The American contingent in Houston enjoy themselves at the players' party Sunday night.

#NextGenATP Americans Reilly Opelka, Frances Tiafoe, Jared Donaldson and Ernesto Escobedo attend Kids Day in Houston.

Introducing the Miami 2017 ATP University graduating class!

[L-R:] Taylor Fritz, Daniil Medvedev, Borna Coric, Karen Khachanov, Reilly Opelka and Stefan Kozlov at the register for tickets launch event in Indian Wells for the Next Gen ATP Finals, to be held in Milan, Italy in November.

[L to R:] Taylor Fritz, Daniil Medvedev, Borna Coric, Karen Khachanov, Reilly Opelka and Stefan Kozlov take part in the tickets launch event in Indian Wells for the Next Gen ATP Finals, to be held in Milan, Italy, in November.

Taylor Fritz, Daniil Medvedev, Borna Coric, Karen Khachanov, Reilly Opelka and Stefan Kozlov attend the #NextGenATP event in Indian Wells.

The triple towers of the Memphis Open: 6'10" John Isner, 6'11" Ivo Karlovic and 6'11" Reilly Opelka.

Frances Tiafoe, Benjamin Becker and Reilly Opelka meet American football star Ty Montgomery and basketball legend Dirk Nowitzki at the Dallas Challenger.

Reilly Opelka is all smiles after winning his first Challenger title in Charlottesville.

¡Atlanta puede haber encontrado finalmente a una aficionada más alta que Reilly Opelka!

Reilly Opelka y Tommy Paul ganaron el primer partido de dobles de sus carreras en el ATP World Tour ante Monroe/Skupski en Houston el lunes.

Reilly Opelka throws out the first pitch at the Chicago White Sox game.