Mesoraco left before the seventh inning due to dizziness from being overheated, and Phillips left entering the eighth inning with a mild strain in his left calf.
Mesoraco was replaced by Ryan Hanigan, and Phillips, who hit the game-winning solo home run in the seventh, was replaced by Wilson Valdez, who moved to second from shortstop. Zack Cozart subbed in for Valdez at shortstop.
While the club pegged Phillips' injury as a "minor" strain, the All-Star second baseman said his calf may be more serious than he initially anticipated.
"The calf is no bueno right now," Phillips said. "Dr. [Kremchek, medical director] looked at it, and he said it was worse than what they expected. I didn't know. I just knew it felt bad. I just feel like I let people down, especially because we're in first place and the race is real close. You already have one person out, so I don't want to be the person coming out. It just really [stinks]."
This is the second time in three days that Phillips has made an early exit after he left Sunday's game against the Rockies in Colorado in the fifth inning with a cramp in his calf. He returned Monday and played the full game.
"I tried to play [Monday], because the win streak was gorgeous and I wanted to keep it going, so I tried to man up and go out there and play. I hurt it [Monday] just playing, period. The thing is, when I hit, I'm always on my toe and it tightens the calf up a little bit. It just wasn't feeling good."
Phillips cited two different occasions in Tuesday's game where he felt the calf bother him, the first of which came in his first at-bat in the opening frame.
"[Jason Marquis] threw me an inside pitch, and I turned and my front foot didn't turn all the way. It's kind of hard for me to pivot on my front left leg when it comes to hitting. The next thing you know, I aggravated it again on the double play. It just really [stinks]. I mean, you're playing good and the last thing you want to do is go down."
Phillips was 1-for-4 with two runs and an RBI before leaving the game and has been an integral part of the Reds' offense since moving to the third spot in the order following Joey Votto's injury. He is hitting .327 in that 13-game span with three homers and 12 RBIs, and he is hitting .368 since the All-Star break.
"I didn't tell anybody on the team, I just wanted them to go out there and just keep playing the way they're playing, don't worry about me," Phillips said. "Keep the attention off me and everybody just keep doing what they're doing. Now everybody has learned about it instead of going out there and worrying about winning. Hopefully they can go out there and keep on winning without me for a while."
Mesoraco, who was ejected from Monday night's game for arguing with the umpire, was 0-for-3 before his exit.
Mark Clements is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.