HOUSTON -- In the roller-coaster world that has been the Mariners’ bullpen, Dan Altavilla might be the poster boy for the topsy-turvy nature of this season.

Expected to be one of the mainstays of the rebuilt relief crew in Spring Training, he opened the season with the Mariners in Japan but wound up being sent down to Triple-A Tacoma and eventually demoted to Double-A Arkansas after his command escaped him.

The hard-throwing 26-year-old returned in late June and seemingly had rediscovered his form -- and upper-90s fastball -- but that success was quickly derailed by a strained right forearm.

Now it's September, and Altavilla is one of the late-season callups looking to stake a claim in the future plans and again is showing signs of why he could be part of things going forward. He looked extremely sharp in striking out the side in the ninth inning of Thursday’s 11-9, 13-inning loss to the Astros.

Altavilla set down American League Rookie of the Year candidate Yordan Alvarez, the red-hot Yuli Gurriel and Aledmys Diaz with a flurry of 98-mph fastballs and wicked sliders, the combination that had made him one of Seattle’s up-and-coming bullpen prospects in prior seasons.

“I thought Altavilla threw the ball great,” manager Scott Servais said. “He’s really cleaned up mechanically and simplified things. For him, as hard as he throws, it’s just staying on line and getting everything going at the catcher versus a lot of twisting and spinning off and losing release points and having no consistency with it.”

Altavilla says that he made a mechanical adjustment in late June, a week prior to injuring his forearm, changing how he was setting up on the rubber.

“It gives me better direction, and it’s working so far,” Altavilla said. “I think even before I got hurt, I was in a good spot. It was a quick adjustment coming back. Now it’s just a matter of staying healthy and getting a consistent opportunity.”

Altavilla, the Mariners’ fifth-round Draft pick in 2014 out of Mercyhurst College in Pennsylvania, has shown flashes before. He put up a 0.73 ERA in 15 games as a rookie in 2016 and had a 2.61 ERA in 22 outings last season, but he has dealt with injuries and has bounced back and forth between Tacoma and Seattle most of the past three years.

But Servais says the stocky right-hander is throwing as well as he’s ever seen during his time with the club, and clearly the Mariners are searching their bullpen ranks for help going forward. This season didn’t go exactly as Altavilla had planned, but he’s learned from his experiences.

“Going to Japan, coming back and getting sent to Tacoma and then Arkansas, back to Tacoma, to the big leagues, it’s been a crazy year,” Altavilla said. “But any year you’re here is a blessing. I’m just looking to make the most of my September, finish the season strong and hopefully create an opportunity for next year.”

Worth noting

• The Mariners will juggle their rotation slightly, with Felix Hernandez getting bumped up to pitch Sunday’s series finale against the Astros, pushing rookie Justus Sheffield back to Tuesday’s game against the Reds in Seattle.

Hernandez pitched three innings in his most recent start, on Tuesday against the Cubs, and will remain on his usual four days’ rest thanks to Wednesday’s off-day. But Sheffield will now have an extra three days between starts as the Mariners look to be careful with his work load while also having him avoid the high-powered Astros at Minute Maid Park in what will be his fourth Major League start.

• Catcher Omar Narváez wasn’t in the lineup for a fourth straight game as he recovers from a back issue, but he pinch-hit on Thursday and was available off the bench again on Friday.

“He may DH or catch [on Saturday] and probably will catch one of the last two games here this series,” Servais said prior to Friday’s game. “He’s feeling better. He was locked up pretty good there for a couple days, just a muscular thing with the back.”

• Servais had no update on right fielder Mitch Haniger, who is seeking a second opinion on his own lower back issues as he looks to see if it’s still possible to return this season after missing the last three months with a ruptured testicle and now a back problem.