PHOENIX -- Two relief appearances, two dominant outings, two wins. Justus Sheffield has quickly emerged as another back-end bullpen option for Mariners manager Scott Servais down the stretch.

“Sheff thinks he can probably win 20 games doing it this way,” Servais quipped after Friday’s 6-5, 10-inning victory over the D-backs.

The 25-year-old left-hander has been impressive so far. After missing nearly two months due to a left forearm strain and a Grade 2 oblique strain, Sheffield returned to Seattle and promptly tossed a scoreless sixth inning on Wednesday against the Astros. In the bottom of the frame, the Mariners scored the lone run of the game on an Abraham Toro sacrifice fly.

Sheffield made his second relief appearance on Friday, retiring Arizona in order in the bottom of the ninth to send it to extras. In the 10th, Jarred Kelenic lifted Seattle to victory with a go-ahead RBI single.

Between the two outings, Sheffield faced the minimum six batters, needing only 30 pitches and landing 21 for strikes. He’s simplified his pitch mix, using only his sinker/slider combo while abandoning his changeup and his four-seam fastball, the latter of which he rarely used anyway (nine times in 2021, per Statcast).

When Sheffield was rehabbing with Triple-A Tacoma, he made two starts in mid-August. Then, the decision was made to utilize him as a reliever. In his first relief outing on Aug. 26 against Salt Lake, he allowed three runs (two earned) on three hits and one walk in one inning.

Sheffield said he had tried to carry over his mentality as a starter. He ditched that the next time out.

“I was just like, ‘Man, forget it. I’m about to come out, just be a dog out there, let it fly.' I’m only out there for one inning, or however many innings. Just let everything eat. Rip the slider. Throw the heaters in. And just let it eat.” Sheffield said. “That’s kind of what everybody’s been telling me.”

It immediately produced better results, as Sheffield tossed a 1-2-3 inning with a pair of strikeouts last Sunday against Salt Lake, his final rehab outing. And he’s now carried that over to his big league return.

A former top prospect, Sheffield has had mixed results early in his Major League career as a starter. In 2019, he went 0-1 with a 5.45 ERA in his first seven big league starts. He had a better showing in ’20, going 4-3 with a 3.58 ERA in 10 starts, but he went 5-8 with a 6.48 ERA in 15 starts earlier this season.

But for now, Sheffield is going to be used in high-leverage relief spots as the Mariners try to make a late push into the postseason. Servais doesn’t plan to pitch Sheffield on back-to-back days, because of his limited relief experience, but Servais also noted that Sheffield would do it if asked -- just another way he’s showing he’ll do whatever it takes to contribute down the stretch, even in an unfamiliar role.

“He’s simplified it -- ‘I’ve got to throw strikes, I’ve really got two pitches to do it with and go after the hitters,’ and it’s worked out pretty good for him,” Servais said. “So I really appreciate that attitude. Not all guys are wired that way. In his mind, I know he still believes he’s a starting pitcher, but the best thing for our team right now is being able to have him out of the bullpen, and he’s really embraced it, he’s got no problem with it.”

However, Sheffield has made it clear that his goals haven’t changed for 2022 and beyond.

“I’m going to come in next year as prepared as ever to be ready to get a spot in the rotation,” Sheffield said.