SEATTLE -- When Major League Baseball rolled out its “Let the Kids Play” promotional campaign this year, the Mariners clearly took them seriously, starting seven rookies in Thursday’s 11-5 loss to the Reds at T-Mobile Park.

With those kids come some growing pains, as evidenced by right-hander Justin Dunn, the club’s No. 5 prospect, walking five batters and lasting just two-thirds of an inning in his MLB debut.

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But there also comes youthful energy and untapped potential, which right fielder Kyle Lewis flashed again as the 24-year-old continued his impressive introduction by going 3-for-5 with a double and his third home run in his first three games.

Lewis unleashed a 457-foot blast leading off the fifth inning, the longest Statcast-recorded home run of the season by a Mariner, and joined Trevor Story of the Rockies (2016) as the only players to homer in each of their first three career games in MLB history.

“I don’t think about it as crazy,” Lewis said. “I just try to play my game, day by day. Things like that are kind of more external. I try to remain internal, if I can, and continue to play my game.”

Lewis, the Mariners’ first-round Draft pick in 2016, is now 5-for-11 with three homers, a double and five RBIs since being called up from Double-A Arkansas on Tuesday.

After Lewis homered off a pair of fastballs in his first two games, he saw nothing but curveballs in his first two at-bats Thursday. But the youngster ripped a leadoff double in the second and singled in the third off starter Tyler Mahle, then got a 94 mph fastball from reliever Lucas Sims in the fifth and launched it over the out-of-town scoreboard.

“He’s obviously seeing the ball really good and not overthinking,” manager Scott Servais said. “The thing that’s stood out for me is he’s in the moment. He’s not looking ahead, he’s not looking behind. He’s just there, playing the game and trusting his ability.

“I love to see a young player come to the big leagues like that and get off to the start he has. He looks very comfortable, like he’s been here a long time, which is a great way to look when you’ve got three games under your belt.”

Shortstop Donnie Walton recorded his first MLB hit with a second-inning single, utility man Dylan Moore continued his solid season with a two-run homer and fellow rookies Shed Long and Braden Bishop each chipped in with hits as well as the first-year players accounted for eight of Seattle’s 11 hits.

The seven rookie starters, including Dunn on the mound, equaled a franchise record set back in 1983 when Harold Reynolds was one of the newcomers. The Mariners overcame Dunn’s shaky start to take a 5-2 lead into the seventh, but the Reds rallied behind three late homers -- including a Freddy Galvis grand slam -- to avoid a series sweep.

Dunn acknowledged his adrenaline was overflowing when he took the big league mound for the first time. The 23-year-old had just 39 walks with 158 strikeouts in 131 2/3 innings at Arkansas this year, but couldn’t find his command or slow things down in his debut.

“There were a lot of jitters. You want to impress, obviously, and show you deserve to be here,” Dunn said. “But at some point you have to get past that and fill the zone up.”

“I thought his stuff was fine, he was just amped up,” Servais said. “He’ll learn from it. We’ll give him another shot in five or six days when his turn comes up again and he’ll be much better next time out.”