DETROIT -- As the Mariners’ bullpen has undergone a dramatic facelift over the course of the season, one of the many midseason additions has been the welcome return of right-hander Sam Tuivailala.

After undergoing surgery to replace a ruptured right Achilles tendon last August, the 26-year-old battled through the rigors of rehab for much of this season until finally rejoining Seattle in mid-July. In seven appearances since, he’s posted a 2.45 ERA with nine strikeouts and three walks in 7 1/3 innings.

While Tuivailala's mid-90s velocity isn’t quite 100 percent back, he’s throwing consistently in the low 90s and showing life on his pitches. In short, he’s done exactly what the Mariners were hoping in this first season back from such a difficult surgery.

“I like the way he’s throwing,” manager Scott Servais said. “I don’t think we’re seeing his top-end velocity yet and that doesn’t surprise me. I think there’s more in the tank as he continues to gain confidence and get comfort in where he’s at physically. But I think he’s throwing the ball really well.”

The 6-foot-3, 225-pounder is aware of his velocity, but not concerned, either. Tuivailala is pitching effectively and the fastball, slider, curveball combination are working well.

“The velo is always fluctuating. It’ll be from 92-95,” Tuivailala said. “It’s definitely something I want to improve on, but all that comes with strengthening the back side. I’m still doing stuff with the Achilles, and when I get that flexibility and strength back in my ankle, I think everything will be fine.

“Everything feels right. I feel strong, but it’s just little stuff with my push-off leg that will be better when I can rest it in the offseason, and then obviously strengthen the areas I need to. I’m not worried about it all.”

For Tuivailala, just being back pitching in the Majors was the primary goal, and the fact he’s pitching very well is a definite bonus.

“Everything is feeling better and better every time I get back out there,” he said. “I’m trying to just get the flow of everything. Every time I get out there –- long toss, games –- it’s all coming back. I’m feeling pretty good right now.”

Seattle has used Tuivailala twice as an opener, and he’s thrown two scoreless innings, but he’ll primarily be used as a setup man in a bullpen that has just two pitchers remaining who started the season with the team in Japan in March.

“The whole goal was to get him back out there this year, and hopefully he’ll keep feeling healthy,” Servais said. “We’re going to be careful how much we use him. We’re not going to run him into the ground. We want to be very cautious. If he goes out and has a good inning, he’ll probably have a day off and go that way here toward the end of the season."

Tuivailala certainly figures in the Mariners’ bullpen plans going forward, so the final six weeks of the season will set him up for 2020 and beyond.

“It’s definitely been a long journey,” he said. “I missed a lot of time, so I just want to finish strong right here. I’m happy to finally be back with the guys, and be in this atmosphere and able to compete with them. I’m happy and want to finish strong.”

Worth noting

• Felix Hernandez’s third rehab outing is Wednesday for Class A Short-Season Everett, which hosts Tri-City at 7:05 p.m. PT at Funko Field. The veteran right-hander has been sidelined for three months with a right shoulder issue, and he threw two-plus innings and 41 pitches his last appearance for Class A Advanced Modesto.

Servais said the goal is to stretch Hernandez out to four innings in this outing and then ramp up to five frames in a start for Triple-A Tacoma before seeing if Hernandez is ready to rejoin Seattle.

• The Mariners are leaning toward an “old-school bullpen day” on Saturday in Toronto, according to Servais. That will be the first time they need a fifth starter since trading Mike Leake on July 31.

The other option would be calling up someone from the Minors, with Justus Sheffield the logical choice, though Seattle could wait on Sheffield until September and just go with relievers on Saturday since the Mariners have nine pitchers in the bullpen.

That likely will depend on how heavily Seattle leans on its 'pen during the Thursday afternoon series finale against the Tigers, since that would be the last day to make a decision in time to get someone promoted to Toronto by Saturday if needed.

• Dan Altavilla threw a perfect inning with two strikeouts in his first rehab outing for Everett on Sunday as he returns from a five-week stint on the injured list with a right forearm strain.