"I'll fluctuate between Fields and Lo based on the workload previously leading up to that," Porter said. "It's a good option to have both of those guys pitching well."
Lo, who got his first save Tuesday in Oakland, was warming up to pitch the ninth inning of a two-run game Friday night before the Astros broke it open with a three-run homer by Chris Carter and a solo shot by Matt Dominguez. Still, Porter let Lo handle the ninth because he was warmed up.
"In that situation, you want to bring your closer in," he said. "Once you get the three-run homer, I made that decision. I'm not going to sit him back down and he's coming into the game."
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.