(Matt Slocum / Associated Press)

Late last season, the Oakland A’s moved minor league lefty Ian Krol from the rotation to the bullpen, adhering to the 100-inning limit they had placed on him after arm problems the year before. Krol had always thrown his fastball between 88 and 91 mph. In his third appearance as a reliever, Krol turned around and saw a “96” flash on the radar gun.

“I was just like, ‘Whoa. Where’d that come from?’ ” Krol said. “I didn’t even think was possible to even sniff 96. I guess something must have happened. My arm was liking the relieving a lot better than the starting role. It was pretty insane to see 96 up there on the scoreboard. I never thought I would hit 96 in my life.”

The random moment last August at Class A Stockton has improbably come to have a major effect on this Nationals’ season. After Krol’s relief epiphany, the Nationals landed him as the player to be named later in the three-way trade that sent Michael Morse to Seattle. Krol kept firing aspirin tablets in Class AA Harrisburg, and in early June the Nationals summoned Krol to the majors.

Krol, in both performance and presence, has been the biggest key in the stabilization of the bullpen, giving Manager Davey Johnson the left-handed stopper the Nationals disregarded over the winter. Krol has struck out 12 in eight scoreless innings, and along with Fernando Abad has given Johnson options and taken pressure off Tyler Clippard, Drew Storen and Co.

“I haven’t really earmarked exactly, all the weapons I’ve got, how I want to line them up,” Johnson said. “But I’ve got a lot of options now, which I like.”

The Nationals’ bullpen lost its way with Zach Duke as the only left-handed reliever for the first two months of the season. With Krol’s addition, the bullpen has again become a strength. Since Krol arrived June 4, the Nationals have a 2.23 bullpen ERA.

It is not a coincidence. As Krol and Abad have matched up against opponents’ best left-handed hitters late in games to set up Rafael Soriano, Johnson can better employ Tyler Clippard, who had been used as a de facto lefty because of his devious change-up. Back to his old role, Clippard has allowed one run in 9 2/3 innings in June.

Krol and Abad have helped align the bullpen, and no reliever has been more impressive than Krol, a 22-year-old whom Oakland took in the seventh round in 2009. Krol has overwhelmed left-handed and right-handed batters alike. Opponents are 1 for 27 with a walk and 12 strikeouts against him.

Krol has not messed around. He fires his mid-90s fastball inside, right on the hands of hitters. He will occasionally mix in his change-up or curveball, but he always comes back to his fastball, which has been super-charged since he became a reliever. Along with the velocity, Krol’s short-arm delivery prevents batters from seeing the ball.

“You see good hitters taking pitches down the middle,” Johnson said. “His ball comes out of his hand, and they don’t pick it up that good.”

Krol has quickly earned Johnson’s trust late in games. One of the more striking features of Krol has been his calm. He never expected to be in the majors this quickly – he was not even in major league spring training. But now that he is here, he has not let the stage affect him.

“If I was nervous, you would be able to tell, for sure,” Krol said. “My mother always says, ‘You don’t look like you’re worried about anything.’ She knows if I was, she would be able to tell. I just go out there and try to slow everything down, only do what I can to my capabilities. I don’t try and do too much. I don’t try and be too fine with my pitches. I just go out there and act like it’s a regular baseball game. I’ve been doing the same thing for years, going out there and throwing.”

A year ago, Krol was a starter in High-A out in California. Today, he is a crucial piece in the Nationals’ bullpen and has helped revitalize a contender. It has not quite sunk in yet, but it has not been too much for Krol.

“It’s nice to know Davey is confident putting me in those situations,” Krol said. “You know, it’s fun. It’s what we live for, really.”