The Astros went 2-8 on their longest homestand of the season to fall to 10-28.
"We didn't play well enough to win, and when you don't play well enough to win, you have to figure out, 'OK, how can we play better?'" Porter said. "The games that are more gut-wrenching are when you play well enough to win and you don't get that one break point that gets you over the hump."
Lyles, making his third start since returning from Triple-A Oklahoma City, gave up four runs in the third inning, including a two-run homer by David Murphy, and three more in the fourth before being pulled from the game in favor of Edgar Gonzalez, who joined the club Sunday after Philip Humber was cut loose.
"He just didn't have his fastball command," Porter said. "Against a ballclub like the Rangers -- they're a good-hitting team anyway -- you fall behind in the count and you put fastballs in the zone, they're going to do pretty much what they did today."
It was a step back for Lyles (1-1), who had given up 10 hits and five runs in 10 innings in his first two starts since getting called up.
"Didn't go as planned," Lyles said. "I wasn't throwing the ball over the plate. Missing by a little bit, missing by a lot. They hit me around pretty good and then I walked some guys and then they hit me around some more. Overall, I've got to do a better job not letting the bullpen throw that many innings. The loss today is definitely on my shoulders, and I definitely have to do a better job of competing."
Lyles said he had no command of his breaking stuff.
"I think I maybe threw three or four offspeed pitches in the strike zone," he said. "My curveball was horrific today. Maybe I can bounce back from this and get on a little run, but secondary pitches today ... I definitely need to turn that around next outing. "
Porter said it comes down to experience for the 22-year-old Lyles, as well as learning to trust his stuff. Sunday marked his 43rd big league start.
"There's a lot of guys who have the stuff, but if you don't trust your stuff, that's a different story," Porter said.
Texas scored four more times in the fifth against Gonzalez to take a 12-1 lead, including a leadoff homer by Leonys Martin and a three-run blast by Adrian Beltre. The Rangers hit nine home runs in the series -- three in each game -- after hitting just 14 in their first 19 road games this season.
"No matter who we're playing, we're trying to win," Beltre said. "The Astros may not be playing the best ball, but they got guys over there who want to win. We had to come here and produce and we did. It's always nice to sweep, whether it's the Astros, Angels or Oakland. It's not easy just because it's the Astros."
Rangers starter Nick Tepesch (3-3) allowed one run and four hits and struck out eight batters in six innings. The only run he allowed came in the fourth, when Astros catcher Jason Castro hit a line-drive home run just over the right-field wall.
The Astros, who trailed 8-3 in the eighth inning Saturday before putting the go-ahead run on base in the ninth, watched their bats come alive again late in the game. They scored four in the eighth against Derek Lowe, including a three-run homer by Chris Carter, and added a two-run homer by Brandon Barnes in the ninth.
"It's hard to battle back when you get down 10 runs and you're late in the game and you just try to do what you can to score a run here and there," Carter said. "We ended up scoring six late in the game, but it wasn't enough."
Gonzalez actually settled down and threw three scoreless innings after the rocky fifth, but the hole was too deep.
"There's some days where the other team scores two runs and we don't score any for our pitchers," Barnes said. "That's just how the game rolls, and we're starting to swing the bats a lot better lately, it's showing."