SEATTLE -- The Kumar Rocker Era began with pressure.

The Rangers’ No. 2 prospect, who has dealt with a career’s worth of adversity before ever stepping on a big league mound but made it up to The Show after just 16 Minor League appearances, did not flinch.

“I think this is a very mature, poised player, who knows exactly what he needs to do to be successful,” Rangers general manager Chris Young said before the game. “That happens for different players at different times, and I have no doubt that Kumar is ready for this moment.”

He showed it Thursday.

Backed into a corner to begin his Major League debut, Rocker clamped down to get the Rangers out of a jam, and went on to give Texas just about everything it could have hoped for in his four-inning start, finishing with seven strikeouts and allowing one run in a 5-4 win over the Mariners at T-Mobile Park.

“That was one of the more impressive debuts I’ve seen,” Rangers manager Bruce Bochy said.

Victor Robles lined Rocker’s first pitch in the bottom of the first inning back up the middle for a leadoff single. One pitch later, Julio Rodríguez sent a soft grounder through a hole in the right side of the infield -- and then proceeded to steal second, putting two Mariners in scoring position with no outs.

Then Rocker, the first player of Indian descent to appear in a Major League game, went to work.

“It was time to play baseball early,” Rocker said. “There was no easing into it; we got right to it.”

Cal Raleigh was his first strikeout victim, looking at a 97.1 mph fastball on the inside corner. Then came Randy Arozarena, who fouled the first two two-strike offerings before swinging through Rocker’s vaunted slider. Luke Raley tagged the first pitch he saw to right field, but it went straight to Travis Jankowski, getting the rookie starter out of his first big league jam in his first big league inning.

“We know about his stuff,” Bochy said. “You look at what he was doing in the Minor Leagues, and that’s why he’s up here. But what stands out is his composure, the poise he showed out there.

“That first inning, trust me, that’s as nervous as you can be, when you make your first Major League start. He didn’t let it get away from him, made pitches. He just looked so focused out there.”

Rocker retired the side in order in the second, and got out of the third with another strikeout, filling up a highlight reel with flailing swings by Mariners batters who, for the most part, just could not figure him out.

Rocker recorded 17 whiffs, the most by a Rangers pitcher in their Major League debut since pitch tracking began in 2008 and tied with Max Scherzer’s July 30 outing for most by a Texas pitcher in four innings this season.

Thirteen of those came against his slider -- one off the Rangers’ season high of 14, set by Jon Gray in May. That’s tied for the third-most whiffs on a single pitch in a player’s MLB debut in the pitch-tracking era.

Four of those whiffs classified as swords, with Rocker making a veteran-heavy Seattle lineup look downright foolish.

“[When an] overhand righty that is getting that many check swings or swing appeals, like, you've got to have something special,” first baseman Nathaniel Lowe said.

The 24-year-old’s fastball averaged 96.8 mph, topped out at 97.6, and got three whiffs of its own, though Rocker said he never truly found the command with it he wanted.

“Try to play the situation that it is and play it as it comes,” Rocker said of his mindset. “Take it one pitch at a time; if you try to do too much in those situations, you probably find yourself getting beat. I did what I could with it, and it ended up going in my favor.”

The only blemish of Rocker’s night came on the one hit he allowed after the first two batters of the game, when Justin Turner belted a solo home run to straightaway center on a full-count fastball in the fourth inning.

Other than that, Seattle put just three balls in play with exit velocities above 95 mph; all three went for outs.

With Rocker sitting on 74 pitches after a long fourth inning -- right around his pregame target -- Bochy went to the bullpen going into the fifth.

But in just four innings, Rocker had given the baseball world a whole lot to talk about.

“He had the four-seam and his two-seam, but he really only needed his slider tonight,” second baseman Marcus Semien said. “I know he has other stuff to come -- can’t wait to see his next start.”