Better still, since May 17 he has a 1.35 ERA in 20 innings over 18 games, with 23 strikeouts. During that blissful stretch, opponents are hitting just .208 against him.
"I think I'm just feeling good right now. My arm feels good, body feels good, [I'm] executing my slider," Kelley said. "That's my strength, to get ahead and get guys out with it, and I'm doing that. I'm not having to feel like I have to overthrow or try to do more than I'm capable of.
"More so just being myself."
That's been much easier to do for Kelley since he missed 13 games in late April and early May with a strained left calf.
On Thursday he needed 26 pitches to get six outs and came close to working an immaculate 10th inning, striking out the side on 10 pitches.
"That's the best outing I've seen him have," said interim manager Pat Murphy. "I think that he's getting comfortable. He's on a new team, and he struggled a little bit early, took some time off, [went] to Triple-A [on an injury rehab assignment] and came back up.
"He knew what he's capable of, and now he's found himself."
Kelley, who had a 10.13 ERA in six games in April, has flourished after rediscovering his slider, a pitch he uses often to both right-handed and left-handed hitters.
Of the 26 pitches he threw on Thursday, eight resulted in a swing-and-miss -- three on fastballs, five on sliders.
Kelley has also been able to give Murphy and the Padres something they've lacked for a while -- someone who can work multiple innings in relief. His last two outings have each covered two innings.
"I'm the long man," Kelley laughed. "No, it's good and bad, because sometimes you have a long man that might sit down there for a while. You're afraid to use him, because maybe the next day you might need innings.
"It's not ideal; you don't go into a game hoping to throw two or three innings. But when you do and it goes well, you're happy about it."