Reilly Opelka first crossed paths with Taylor Fritz on the junior tennis circuit as a 14-year-old. They were two lanky teenagers with booming serves and an eye toward tennis stardom. Yet he could have hardly predicted what would happen just four short years later.

Opelka is now a junior Wimbledon champion after winning the title last year and Fritz has been the youngest player in the men’s top 100 since late February. Both are considered to be in the next generation of top American men’s tennis players.

Those are fine accolades, but what happened off the court earlier this month is possibly the most surprising to Opelka. At 18, Fritz got married to fellow tennis player Raquel Pedraza in a ceremony in California. And the best man? Reilly Opelka, also 18.

“No,” Opelka said Tuesday after his first-round singles loss at the Citi Open. “I wouldn’t have guessed at 14 that a couple years later I [would be] his best man.” It was the first time Opelka cracked a smile during his post-match interview after he expressed extreme disappointment at his three-set defeat.

Fritz won his first-round match Tuesday, and the pair will play doubles together Wednesday afternoon at the Rock Creek Park Tennis Center.

“That was a huge honor, to be honest,” Opelka said of being the best man. “Since the first time I’ve met him, we just really clicked. … Whenever we travel, I room with him. I think he’s a really good friend to have around. I trust him.”

Opelka, ranked No. 833 in the world, was not the only pro tennis player in Fritz’s wedding party. Tommy Paul, 19, was a groomsman, while fellow Americans Steve Johnson and Mardy Fish were among the family and friends in attendance.

Fritz has rocketed up the rankings to No. 67 and is considered one of the top American hopefuls in men’s tennis. He told Post columnist Dan Steinberg why he decided to get married at a young age and why he surrounds himself with a tight-knit group.

“She’s been with me the whole way, so I really don’t think I’d be where I am now without all of her support,” Fritz said of Pedraza. “She’s such an important member of my team and making everything work with my career, I figured it’d be best for my career. And you look at some of the best tennis players in the world right now – [Roger] Federer, [Novak] Djokovic, [Andy] Murray – all of them have been with the same partner for pretty much their whole life, pretty much from their teen-aged years too.”

At 18, Taylor Fritz has a huge serve and a new wife. Just don’t call him a kid.

Opelka emphasized how much fun it is to be friends with the young Americans on tour. He also considers Paul, Frances Tiafoe, who trained at the Junior Tennis Champions Center in College Park, Michael Mmoh and Stefan Kozlov — all pro tennis players — to be his closest friends.

The players can often be seen posing in photos together or poking fun at each other on social media. It makes their job not feel like work — for the most part.

“It’s really fun being with those guys,” Opelka said. “I like spending time with all of them, on the court and off the court.”