Lyles was pulled after throwing 39 pitches in a laborious fourth inning in which he allowed four runs on two-run singles by Alberto Callaspo and Erick Aybar and suffered the loss in a 7-2 setback to the Angels before 26,650 fans at Minute Maid Park.
"He pretty much just lost fastball command and was not able to get in the zone in a lot of deep counts and was right at close to 40 pitches in that inning, and at that point you're not going to send him back out there to get into another stressful inning," Astros manager Bo Porter said.
The Astros hit the midpoint of their schedule at 30-51, which puts them on pace to best last year's 107-loss season by five games. They've played much better lately, going 20-21 after starting the season with 30 losses in their first 40 games.
The biggest reason for their improved play in the second quarter of the season is the starting pitching. Houston pitchers posted a 5.81 ERA in the team's first 40 games and had a 3.60 ERA in the next 40 games, with Lyles a big part of that turnaround.
Lyles (4-3) had allowed two runs or fewer in seven consecutive starts, but is 0-2 with 9.00 ERA in his last two outings.
"I wasn't good today," he said. "That's it."
Lyles considers himself a fastball pitcher and said he's throwing about 60 percent heaters when he's in a groove. He was falling behind hitters repeatedly with his fastball Saturday.
"I walked a couple of guys and hit a couple of guys and just put myself behind the eight ball," he said. "My secondary stuff has to be good if I'm going to lean on my secondary stuff and forget about the fastball. I've never done that before, so I'm going to need that fastball to be there, and it will in five days."
Howie Kendrick blasted a solo homer off Josh Fields in the fifth inning to stretch the lead to 5-0 for Angels starter Joe Blanton (2-10), who held the Astros to two runs and three hits in seven innings. He's 1-2 with a 2.91 ERA in three starts against the Astros this year.
"He's not afraid to throw anything in any count," Astros first baseman Brett Wallace said. "He's a veteran and has good stuff and mixes and keeps you off balance. He's around the zone but knows how to keep the ball on the corner and keep balls down. He mixes and matches quite a bit."
Wallace socked a two-run homer off Blanton in the seventh -- his first in the Major Leagues since Sept. 28 of last season at Milwaukee. Matt Dominguez followed Wallace with a long fly ball to right that Josh Hamilton reached out and caught at the top of the wall. Hamilton made a similar catch to rob J.D. Martinez of a potential home run to end the fourth inning.
"Even the balls we hit hard, they just happened to make great plays," Porter said. "It's one of those things. All you can do is swing the bat, hit the ball hard and you have no control over whether it gets down for a hit."
Back to Lyles.
His troubles in the fourth began with a leadoff single to Mark Trumbo. He hit Kendrick in the head with a pitch while he was squared to bunt, then walked Hamilton to load the bases. Callaspo ripped a 3-2 pitch up the middle for a two-run single.
"Just a little wild," Lyles said. "The curveball was pretty decent, and I threw a lot of them. I kind of leaned on it, and in the fourth inning I thought I just kind of backed off a little bit and started aiming with the fastball and changeup. The changeup I hit Kendrick in the head with, I don't know what happened there. Just a little erratic in the fourth."
Lyles hit Peter Bourjos in the wrist one out later -- forcing him to leave the game with a right wrist contusion -- to load the bases for Aybar, who stroked a two-run single to right field to make it 4-0.
"He has a good arm, pitched some good ball against us this year," Angels manager Mike Scioscia said of Lyles. "We did a much better job in the batter's box today, working the counts. It still took some clutch hits to get him out of there."