"He plays hard and he wants to play," Baker said. "I had to supersede today what was best for him and what's best for us, because we certainly can't lose anybody else."
Heisey was hit by a pitch Friday and collided with Pittsburgh first baseman Garrett Jones in the seventh. Baker said Heisey has been hurting for a while, and Friday night's events only worsened his status.
The Reds have played with Jonny Gomes, Drew Stubbs and Heisey as their only outfielders since injuries sidelined Jim Edmonds, Laynce Nix and Jay Bruce.
Cairo took the assignment in stride. He hasn't played right field this season and made just his 14th career appearance (third start) at the position.
"It's just another game. That's it. Whatever happens, happens," Cairo said. "You can look in the book."
Cairo delivered a sacrifice fly and was lifted for Heisey as part of a defensive substitution in the eighth. Heisey ended up smacking the game-tying double in the ninth.
Shortstop Orlando Cabrera was back in the starting lineup Saturday after missing the past three games with soreness of the left oblique muscle, a problem that previously had him on the disabled list for a 26-game stretch. He went 1-for-5.
That enabled Baker to use Paul Janish off the bench. Janish has been practicing in the outfield in case he might be needed there as well.
"That's how it's been for a while now," Baker said. "One leaves and one comes back."
Bruce told Baker he could play defensively, but Baker didn't want to take that risk.
"I don't want him doing nothing today so he can give that side a rest because he's been really, really pressing it," Baker said. "He told me he could play defense [Friday] night, which he probably could have, but I didn't want to do that because if they tied up the game then he'd have to hit, and then I'd have no real outfielders left."