"We think he's best suited for that until Pap gets back," Baker said.
Baker soured on the bullpen-by-committee idea after he tried to use matchups to get through the ninth inning of Wednesday night's game against the Cubs. He brought in right-hander Matt Belisle to pitch to righty Kris Bryant, who doubled, then left-hander Oliver Perez to pitch to lefty Anthony Rizzo, who mashed a two-run homer.
"Yesterday was kind of the example that we've never been crazy about bullpen by committee," Baker said before Thursday's game. "Kind of rarely works. So we're going to come up with some semblance of an everyday type situation."
Kelley owns a 2.45 ERA with 35 strikeouts and just six walks in 25 2/3 innings this season. He recorded the final two outs in the ninth inning Thursday after entering the game with runners on second and third. Baker initially wanted to avoid using Kelley, but appreciates the fact that Kelley wants the ball in those situations.
"We talked [Wednesday] for the first time and had that conversation, 'Be ready to work the ninth regardless of the lefty, righty matchup,'" Kelley said. "So I prepare for it just like I do any other time. Now I know kind of how he's thinking."
Baker has also been wary of Kelley's usage considering he has had two Tommy John surgeries. Kelley has pitched in three of the last four games, so he almost certainly will not be available to pitch Friday night.
The Nationals will look at pitch counts, consecutive days and how many times he warms up to determine when he can pitch, and Kelley said that he will have to be honest with how his arm feels, something he is still getting better at.
"I hate being honest, I like to say I can pitch everyday," Kelley said with a smile. "But I will say that I have gotten better."
Jamal Collier covers the Nationals for MLB.com. Follow him on Twitter at @jamalcollier. This story was not subject to the approval of Major League Baseball or its clubs.