"I'd be lying if I said I wasn't trying to strike everyone out as a reliever now, but that's what I'm trying to do," said Kelly, who didn't appear in the Red Sox's 8-7 victory over the Twins. "The scenarios and situations you come into as a reliever, usually, there's a starter who's left a runner or two on base, one or two outs, a guy in scoring position."
The approach clearly worked for Kelly at Triple-A, where he recorded 14 strikeouts and two walks during his transition to the bullpen.
In six starts for Boston this season, Kelly was 2-0 with an 8.46 ERA. He has a 3.25 ERA in 30 appearances as a reliever -- all with St. Louis.
"I know, when I was starting, I wanted the guy behind me to come in and throw his best pitches and try to strike the guy out," said Kelly. "That's what I've been trying to do out of the 'pen."
With Craig Kimbrel and Koji Uehara on the disabled list, Kelly could become an important piece to Boston's bullpen in short order.
"We wanted a fresh arm. A guy that can go multiple innings," said Red Sox manager John Farrell. "And looking to see it in this role play at the big league level. He's throwing the ball well. I think there might have been one outing at Pawtucket where he might not have been as sharp, but it's been encouraging to get the reports that he simplified his attack plan.
"I know he's been aggressive with the approach of attacking hitters and working out of the stretch exclusively, simplifying the overall plan, and we're looking forward to that translating here."
Kelly was optioned to Triple-A Pawtucket on June 1 after a tough start against the Orioles. He injured his right groin not long after and was sidelined for a few weeks.
In Saturday's loss, Hembree gave up three hits and a run over one-third of an inning.
"He's not a confident pitcher right now, and we just did option him to Pawtucket," said Farrell. "As good as Heath has been for the vast majority of this year, really the whole first half, the four times out since the break has been the other side of that."
• The Red Sox expect to have Mookie Betts back in the leadoff spot for Monday night's opener of a three-game series against the Tigers at Fenway.
Betts exited Friday night's game with right knee soreness and has been out of the lineup since.
Farrell said the right fielder could be available for the late innings of Sunday's game.
• Designated hitter David Ortiz didn't play Sunday, as the Red Sox continue to play it smart with their 40-year-old slugger. Farrell is mindful of the fact that the club is in the middle of a stretch of 20 games in 20 days.
• Kimbrel will throw a bullpen session Monday, his first since undergoing left knee surgery July 11. The plan is for him to throw another one by Wednesday, at which point the Red Sox will evaluate whether he's ready to go on a Minor League rehab assignment.