Perez took the loss, allowing five runs in seven innings, and is now 7-8 with a 4.33 ERA on the season. He is 0-4 with a 7.07 ERA in his last six starts and there is one common denominator in the four losses. In each of those starts, Perez had one inning where he gave up at least four runs, and that was the case on Friday night.
Perez gave up four runs in the third, and that was more than enough for Keuchel.
"That seems to be the story for Martin," Banister said. "The challenge is one inning got away. He couldn't slow the inning down."
The inning showed the difference between Keuchel and Perez. Keuchel shut the Rangers down by working both sides of the plate. Perez didn't do that in the third.
"He got away from the fastball inside and that opened up the other side of the plate," Banister said. "It looked like we were a little one-sided. We weren't able to knock some of their hitters off the plate."
The Astros had five hits in the inning, and four of them were by right-handed hitters pulling the ball through the left side.
"A couple of pitches got away and cut back over the middle of the plate," Perez said. "They hit the ball good."
A walk also didn't help.
Jake Marisnick led off the inning with a single to left and George Springer flied out to center. Perez then walked Alex Bregman, the Astros' rookie third baseman and No. 2 hitter who entered the game 2-for-35 since being called up. That helped set it up for Jose Altuve, Carlos Correa and Evan Gattis.
"The concern previously [with Perez] were the walks, and it showed up again with the walk to Bregman," Banister said. "It set up that inning for the heart of their order."
Altuve doubled home one run and Correa singled to drive in two. Gattis and Tyler White followed with singles to make it 4-0 before Perez got Marwin Gonzalez to ground into an inning-ending double play.
Perez responded with three scoreless innings after that, retiring nine of 10 batters. The Astros got one more in the seventh, but it turned out to be not needed. One bad inning brought down Perez on Friday night.
T.R. Sullivan has covered the Rangers since 1989, and for MLB.com since 2006. Follow him on Twitter @Sullivan_Ranger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.