HOUSTON -- Regression is one thing, but Dallas Keuchel's 2016 season is officially beyond that.

Frustration continues to mount for the Astros' ostensible ace, whose struggles this season haven't backed up a breakout 2015 campaign that culminated with an American League Cy Young Award.

It was all on display Sunday, as the Rangers hammered the lefty in a decisive five-run third inning en route to a 9-2 Astros loss and a sweep on Sunday in Minute Maid Park.

It's become an all-too-familiar refrain for Houston. Keuchel struggling on the mound while Texas runs roughshod through the Lone Star Series.

Keuchel now sports an 8.75 ERA (23 ER/23 2/3 innings) in his last four starts against the Rangers, allowing 35 hits with a 1-3 mark in that span.

To listen to the lefty, the diagnosis is simple, if terse.

"Ball is up, in hitter's counts," Keuchel said. "They've done a good job of taking advantage of the mistakes pitchers throw. … I was the one that gave it up, so it's very frustrating."

But more materially on Sunday, it was about Keuchel's execution with two outs, something that has eluded him all season. Texas scored four of its five runs in that third inning -- and five of seven off Keuchel in total -- with two down.

It's an unfamiliar sight, given Keuchel's almost uncanny ability to mitigate high pitch counts with key ground balls or strikeouts last season.

"Just not making pitches with two outs," Keuchel said. "It's very frustrating because I feel like I had some good stuff today, and it showed early. … If I show up on a few pitches here and there, it's a totally different ballgame. It just seems like that's the way it's going right now."

Keuchel was right on that point, as he was dominant the first two innings and still stabilized to survive six innings in total. Still, it's fair to ask: Is the league catching up to him this season?

"It's always a cat-and-mouse game," he said. "Guys know what I'm going to do. If I can get some ground balls like I did [early], I'll take my chances. I could tell them half the time what's coming and I'll be on the best end possible.

"I don't think hitters are catching up to me, it just happens in spurts."

Through 10 starts, Keuchel now sports a 5.92 ERA, a 1.59 WHIP and a 2-6 record. Sunday's loss was his second at home in May. And just compare his numbers in Minute Maid this season to his remarkable 2015 unbeaten run in the building.

Last year at home? Twenty-one earned runs in 18 starts across 129 1/3 innings while going 15-0. As dominant as it gets.

And the 2016 version? It's admittedly a small sample, but he's surrendered 14 earned runs in just 26 1/3 innings and four starts.

On Sunday, it was the bottom of Texas' lineup that hurt Keuchel. They waited him out, laid off some nasty sinkers and sliders and waited for an elevated changeup or fastball. In total, the 6-9 hitters scored four runs on Keuchel and drove in three more.

Astros manager A.J. Hinch called it an "ambush approach," but it hasn't looked a whole lot different when teams have been patient against the star lefty. In fact, Sunday was more proof that, like Houston's season, Keuchel is teetering on the brink of full-blown angst.

"The frustrating part about it is he's a good pitcher, and I don't think he's enjoying the success he deserves," Hinch said. "Some of that is the league adjusting to it a little bit and making it more difficult and some of it is him overcoming these hurdles.

"I still don't like looking up there and seeing our best guy struggle."