Collin McHugh knew he was going to the majors, but until late Monday night, he wasn’t positive what his role would be. He stayed off social media, so he didn’t find out until he ran into pitching coach Brent Strom at the team hotel in Seattle.

“He was like, ‘Yeah, you’re starting, and I was like, ‘OK, alright, here we go,’” McHugh said.

Maybe being in the dark was a good thing, Strom joked.

“For some reason when he warmed up tonight down in the bullpen, he had some exceptional life to his fastballs,” Strom said. “And then his cutter seemed to be working well.”

A 26-year-old righthander who had never pitched for the Astros before Tuesday night, McHugh turned in arguably one of the most dominant outings the team’s seen from a starting pitcher in a decade. The minor-league call-up struck out 12 Mariners in a 5-2 Astros win, their second victory in a row following a seven-game losing streak.

McHugh didn’t walk anybody in 6 2/3 shutout innings and held the M’s to just three hits — all the while throwing only 89 pitches. He entered the game 0-8, making Tuesday even more special because he took his first major league win.

“I’ve had a lot of people encouraging me the last few years just kind of bouncing around a little bit not really knowing where home’s going to be,” McHugh said. “For my wife who couldn’t be here tonight and for my family back in Atlanta, this one’s kind of for them.”

A performance like Tuesday’s leads to all sorts of neat oddities. Only one other pitcher has struck out more batters in his Astros debut: J.R. Richard, who fanned 15 in 1971.

From 2005-14, only four other Astros starters reached 12 strikeouts in a game: Bud Norris (twice), Wandy Rodriguez and Brett Myers. Norris was the last to do it, on June 6, 2012 in a loss to the Cardinals.

As is becoming the norm, the Astros’ offense relied on the long ball Tuesday — three of them. Jason Castro, Chris Carter and Matt Dominguez all went deep. The lineup had 10 hits in all, tying a season-high, but only one run scored on a hit other than a home run.

McHugh was called up Tuesday with the intent of making a start or two in place of Scott Feldman, who has right biceps tendinitis. Losing the ace Feldman, even if just briefly, was a blow. But McHugh more than assuaged the Astros’ worries for a night.