Manager Bobby Valentine sat the third baseman for the second time in four games in an effort to keep his left hamstring healthy. But with the Red Sox needing a spark while trailing 4-0, Valentine called on the rookie, and he delivered with his 14th homer of the season.
"When you're put in that situation and you're a pinch-hitter your job is to drive in runs," Middlebrooks said. "When you're not starting, about the sixth inning you start getting ready, go down in the cage, take some flips, just get loose because you never know."
Middlebrooks attacked the first pitch he saw from Ryan Dempster and barely lifted it over the Green Monster. It was the first pinch-hit homer of his career in three chances.
"I hit it off the end a little bit and I knew at least it was going to hit the wall, so I was running hard out of the box trying to at least get a double for sure," Middlebrooks said.
The umpires reviewed the play but did not reverse the call. The three-run shot made it 4-3. But the Rangers scored once in both the eighth and ninth.
Before the game, Valentine explained why Middlebrooks was not starting.
"I'm counting on him playing in a lot of games here. With the day game and the travel day [on Wednesday] I figured this was a good little breather," Valentine said. "Other guys will get theirs I hope."
Middlebrooks was also out of the lineup on Saturday against Minnesota, though he entered the game in the ninth inning.
"I feel fine, I'm good to go," Middlebrooks said before the game.
Still, Valentine is being careful not to aggravate Middlebrooks' left hamstring, which has bothered him at times this season.
"It's just in the back of my mind," Valentine said. "He's running really well now, showing us enough that we're letting him go on the bases and things. I'm trying not to get him into a fatigue situation where the way he's playing might cause a situation."
Nick Punto started at third base and hit ninth. He was 0-for-2 before Middlebrooks pinch-hit for him.