Pierre, who went 0-for-5 in Friday night's 7-5 loss, had started 63 of the team's 66 games this season, but was relieved by Brent Lillibridge in left field.
"The way he plays," Guillen said, "he needs a day off once in a while just to recover his body and his arm."
A.J. Pierzynski also got the day off behind the plate, but Guillen said that was strictly so he would be ready for Sunday's day game.
Adam Dunn, who entered the day just 1-for-44 against lefties, remained in the starting lineup at DH, hitting sixth. Guillen said he had narrowed it down to giving either Dunn or Pierre the day off, but went with Pierre, who had started 40 straight games since April 28.
"I had to choose between Dunn and Juan Pierre, and I chose Juan Pierre, because every time Dunn is on the bench, the boss is losing a lot of money," Guillen said with a laugh. "But no, I just think Juan needed a day off more than Dunn."
Despite 22 of his 23 starts coming in the outfield this season, it was only the third career start -- all of which have come this season -- in left for Lillibridge, who made a game-saving catch in eighth to rob Coco Crisp of a two-run home run.