Celtics rookies Grant Williams, Carsen Edwards throw out the first pitch at Red Sox game

Boston Celtics rookies Carsen Edwards, left, and Grant Williams, right, throw out the ceremonial first pitch prior to the first inning of a baseball game at Fenway Park.Charles Krupa/Associated Press

Celtics rookie Grant Williams had quite the stage for his first-ever attempt at pitching a baseball.

“I’m actually very nervous for it,’’ Williams said shortly before the moment Tuesday night. “Walking up to the mound, I’m going to be nervous. My hands are going to start sweating.’’

Prior to Red Sox starter And­rew Cashner’s 93.7-mile-per-hour fastball to open the first inning against the Kansas City Royals, Williams and teammate Carsen Edwards took the mound at Fenway Park to deliver the ceremonial first pitches.

The two, donning customized Sox jerseys with their last names printed across the top, were greeted with hearty cheers and applause from fans — several of whom had requested photos and autographs earlier in the day.

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Neither one hit the strike zone, with Williams sinking his low near the dirt and Edwards sailing his high and away. Williams equated his throw to an “eephus pitch,’’ an old term used to describe a low-speed circus pitch.

“Mine stopped a little bit short,’’ he said, with a smile.

The evening’s festivities started well before game’s scheduled start time of 7:10 p.m., as the two spent a couple of hours visiting iconic spots in the ballpark. Edwards was joined by his brother and girlfriend, while Williams was joined by his father, uncle, and agent.

Up first was a trip to the Samuel Adams Deck for a meet and greet with fans and the Larry O’Brien trophy. The session was followed by batting practice, where Williams rattled off a few facts about Fenway and surmised he could definitely hit a home run due to the park’s dimensions.

As the Royals went through their usual routines, Williams also took a few minutes to FaceTime teammate Tacko Fall, who is in his home country of Senegal. Once Fall was on the line, he held his phone up to a group of fans who immediately began chanting, “Tac-ko! Tac-ko!’’ from behind the netting.

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Williams and Edwards also briefly chatted with Red Sox right fielder Mookie Betts, who has been spotted watching Celtics games at TD Garden on multiple occasions.

Later, the pair made their way over to the Green Monster, where they went inside to sign their names on the wall and posed for photographs in front of the scoreboard. Edwards jokingly motioned as if he had just made a catch on the warning track, and Williams played catch with his uncle.

The trip to Fenway Park marked Williams’s second since getting drafted by the Celtics in June. Earlier this summer, he sat on the Green Monster to watch Liverpool take on Sevilla in a soccer friendly.

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The 20-year-old said he has been enjoying his time exploring the city and hopes to do so even more now that he has officially moved in.

“Now it’s more so about under­standing where things are in the city, how to get around,’’ Williams said. “I’ve made a lot of U-Turns and a lot of rights that I should have made lefts.’’

With four Celtics — Jaylen Brown, Marcus Smart, Jayson Tatum, and Kemba Walker — participating in Team USA training camp in Las Vegas this week, Williams and Edwards are helping hold down the local contingent at the Auerbach Center.

“We’re goofy,’’ Williams said. “Me and Semi today were just goofing around. Carsen’s probably the biggest goofer of them all. It’s going to be a great year chemistry-wise and great on the court because we have a lot of talented players.’’