Pence, who was 1-for-8 in the first two games of the series in his hometown of Arlington, hadn't had a day off since June 4, but Keppinger had started 36 consecutive games. He hadn't had a day off since May 18, when Kaz Matsui filled in for him.
"It has been a long stretch for both of them," Mills said. "This is nothing against either of them, but the combination of them being out there for so long and the heat as well, that's tough. Hunter was all over the field [Saturday] defensively and offensively, and it took its toll."
The Astros and Rangers played in 95-degree heat on Saturday afternoon, and the first pitch Sunday was 96 degrees.
Keppinger entered Sunday in an 0-for-10 slump and was hitting .245 in June. Michaels is 9-for-22 with eight RBIs in his past nine games.