So far, so great: White Sox rookie righty Matt Foster off to nearly flawless start

There’s no getting around how big a loss Aaron Bummer is for the White Sox’ bullpen.

And there’s no getting around how big a gain Matt Foster could be.

Granted, Bummer is a left-hander and Foster a righty who hasn’t ascended to the type of game-on-the-line situations Bummer gets paid to handle. But any strength in numbers the Sox can cobble together to get through however long Bummer is sidelined with a sore left biceps is more than welcome.

Foster has only made five appearances, but manager Rick Renteria’s trust in him for high-leverage situations is growing with each one, and why not? He has struck out 13 of the 26 Royals, Brewers, Indians and Tigers batters he has faced and hasn’t been scored on yet.

“He’s fearless,” Renteria said. “He’s got a lot of guts. He’s got some stuff that can get some swing-and-miss. He’s got a presence on the mound that’s calm. He has enough stuff and enough guts and enough command and enough knowledge. He’s capable of doing a very nice job.”

A 20th-round draft pick by the Sox in 2016, Foster, 25, hasn’t given up squat, allowing two hits and two walks in 7⅔ innings. The keys have been a riding 94 mph four-seam fastball, well-located so far, and very good changeup — with an occasional slider thrown into the mix. Lefties are 0-for-9 against him.

Addressing the “ride” on his fastball, Foster said, “That’s definitely something I developed over time. I’ve never been a spin-rate kind of person, looking at stats and numbers, until the last year or two, when I started to see the kind of life I have on the fastball. It plays really well off the changeup, so I can kind of go up and then go down with the change.”

Foster pitched two scoreless innings to open a bullpen day Saturday, then protected a 5-2 lead Tuesday by pitching two perfect innings with four strikeouts in a win over the Tigers that halted a three-game losing streak.

Closer Alex Colome and right-handers Evan Marshall and Jimmy Cordero are the Sox’ most dependable late-inning arms going now, but as opportunities come up for rookies Foster, Zack Burdi and Codi Heuer, “we’ll let their skills speak for themselves,” Renteria said. “They’re building confidence to deal with high-leverage situations.”

In his second major-league appearance Tuesday, Burdi pitched his second scoreless inning, touching 98-99 mph.

“My role right now is to go out there and get outs and throw strikes and be healthy every time they call down to the bullpen for me, and be effective,” said Burdi, who was viewed as a closer when he was drafted in the first round the same year Foster was selected. “We have four or five really strong [established] back-of-the-bullpen guys.”

Foster’s role seems to be evolving and trending upward.

“Every day, I just go out there expecting if I get in the game, I’m going to go do the best I can and try to give my team the best shot to win the ballgame,” he said.