SEATTLE -- Joey Estes had a certain intense look about him as he asked home plate umpire Roberto Ortiz for a new ball after watching Cal Raleigh circle the bases on a home run to begin the bottom of the second inning.

Since his first call to the Majors last season, the A’s have been enamored with Estes’ competitive drive. That intangible attribute was the first thing manager Mark Kotsay mentioned when talking about the 22-year-old right-hander before his season debut on Saturday, and it was on full display after Raleigh’s solo blast.

Following that homer, Estes, Oakland’s No. 11 prospect, locked in and would only surrender one hit the rest of the way. He retired 12 of his final 13 batters, finishing after five innings on just 61 pitches and allowing one run on two hits and no walks with five strikeouts. The solid effort earned Estes his first Major League win in the A’s 8-1 victory over the Mariners at T-Mobile Park.

“It’s awesome,” said Estes, who was doused in a celebratory beer shower from his teammates after the game. “I worked my whole life to be able to say I got a [big league] win. It’s definitely something I’m going to cherish.”

Enhancing the impressiveness of Estes’ outing was the fact that he was pitching with a swollen right bicep for most of it. Facing Julio Rodríguez in the first, the Mariners slugger roped a liner 110.1 mph off the bat that caromed off the glove of Estes before hitting off his shoulder. Estes wasted no time chasing after the ricocheted ball and threw a hustling Rodríguez out at first.

“I don’t know how to describe him really,” Kotsay said of Estes. “You take a line drive like that off the bicep, don’t have trainers come out and don’t want it recognized. He came in the dugout and it was already swollen.

“He pitched four innings after that and grinded it out, which says a lot about the kid.”

Estes’ fierceness on the mound was evident by how he constantly attacked each Mariners hitter. He fired strikes on 40 of his 61 pitches and reached only one three-ball count in his 17 batters faced.

Pounding the zone is nothing new for Estes, who issued just two walks in 10 innings in his two starts with the A’s at the end of last season. This time around, though, Estes carried more conviction, which he said was gained through his previous big league experience.

“When I first got called up last year,” Estes said, “it was one of those things where I couldn’t feel my legs and couldn’t really feel the ball coming out of my hands. For this one, I felt a lot more confident. I’ve been here before. I just felt confident in myself that I belong here.”

Estes was aided by some stellar defense throughout the evening. Lawrence Butler robbed Julio Rodríguez of extra bases in the fourth with a leaping catch at the warning track. One inning later, Brett Harris snagged a 100.6 mph liner at third from Mitch Garver that took away extra bases.

“You can’t ask for much better defense than that,” Estes said. “They’ve got my back and I’ve got their backs, so it was awesome.”

Flamethrowing rookie closer Mason Miller was on track to make an appearance as the A’s took a 2-1 lead into the eighth. But once the A’s broke it open with six runs over the final two innings, including a bases-clearing three-run double by Max Schuemann in the eighth, Miller, who had been warming up, sat back down in favor of Michael Kelly.

The A’s view Estes as a long-term piece of their future, but his promotion from Triple-A on Saturday was more out of necessity with rotation member Joe Boyle recently landing on the injured list with a lower back strain. That’s not to say he can’t take this interim job and pitch himself into more of an established situation.

As Kotsay stated before the game, performance can dictate how long a player stays in the Majors, and Estes clearly has shown he has the stuff to consistently get Major League hitters out.

“Whenever this team needs me, I’m here to give everything I’ve got,” Estes said. “I want to be a part of this team and get wins just like today. It’s a great feeling and a big confidence-booster for me to just go out there, be myself and keep competing.”