Guerrero had two errors in the eighth inning of Game 1 and struggled to cover ground in the large right field at AT&T Park. So the Rangers have opted to start David Murphy in left field and shift Nelson Cruz to his usual spot in right field.
Rangers manager Ron Washington insisted the errors had nothing to do with the decision.
"It didn't play into it," Washington said before Thursday's game. "My main concern with Vlad is I'm trying to keep his bat in the lineup."
Guerrero has been the Rangers' full-time designated hitter in 2010. He hit .300 with 29 homers and a team-high 115 RBIs. Guerrero made 17 starts in the outfield during the regular season but has played in the outfield only twice since the start of September.
Guerrero had trouble racing over to balls hit down the right-field line. The mounds are in foul territory, making fielding balls down the line even more difficult. San Francisco tacked on three more runs in the eighth before Texas answered with three of its own in the ninth in the 11-7 loss.
"He might have missed a couple of balls, but those balls he missed, and if they scored runs off of it, certainly didn't determine the outcome of the ballgame," Washington said. "It might have added some runs but it didn't determine the outcome."
The move does mean that Washington has Guerrero off the bench Thursday if he needs him. Washington said he talked to Guerrero about his decision for Game 2, and the slugger understood what was happening.
"If we come back here for Games 6 and 7, I'm going to play Guerrero a game here too," Washington said. "We're here because of Vlad. So I'm supposed to play two games in San Francisco and not let him touch the field? It won't happen."