By all accounts, Blum has been hot in recent days. Blum, who got the start for the fourth straight game Tuesday, has hit three home runs and collected seven RBIs over the past two games.
But with Bronson Arroyo taking the mound for Cincinnati on Tuesday, Cooper expected to make a switch. Blum is 1-for-15 in his career against Arroyo, hitting .067 with four strikeouts against the right-hander.
Mark Loretta, on the other hand, is hitting .550 all-time against Arroyo (11-for-20) with two doubles and four RBIs.
Cooper said he was planning on giving Loretta the start but could not force himself to take Blum out of the lineup.
"Loretta might have the best numbers of all -- and we had talked before about this is probably a good matchup -- and we wanted to give him the chance," Cooper said. "But when a guy drives in three runs, you better keep him in the lineup. He gets a couple knocks, plays well, you better keep him in there. I would not look too smart to take him out."
Cooper said Loretta will instead get the call off the bench if the Astros need a pinch-hitter against Arroyo.
Blum said he was a bit surprised at the lineup but appreciated Cooper's vote of confidence.
"These last three or four days, I had no idea I was going to be in the lineup," Blum said. "It feels good. I'm glad to be playing when I'm doing well as opposed to when I'm doing awful."
Loretta also could have replaced leadoff hitter Kazuo Matsui at second base. Cooper said he thought long and hard about the situation, but he likes alternating his right- and left-handed hitters in the lineup. Matsui is a switch-hitter, and Loretta hits right-handed.
"My leadoff hitter is doing quite well," Cooper said. We have a day off Thursday, and if not for the day off, I might have done it."
Cooper talked the decision over with Loretta and said the veteran understands the situation.
"You have to go with the hot hand when you can," Cooper said. "Mark's a professional, he knows that. [Blum's] play is performance-based. As long as he's hot, he's playing."
Krysten Oliphant is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.