HOUSTON -- After Ken Waldichuk tossed the best outing of his young career -- six no-hit innings against one of the best lineups in the American League -- the first thing the left-hander mentioned was his three K’s.

“I didn’t really have too many strikeouts,” Waldichuk said with a laugh.

But on Monday night, Waldichuk didn’t need many to mow down the Astros in the A’s 4-0 win at Minute Maid Park. He and opener Mason Miller combined for eight innings of one-hit ball against an offense that entered with the most runs scored in the Majors since the All-Star break.

"This was probably the best pitching performance we’ve had all year,” manager Mark Kotsay said. “The two young kids, Mason Miller and Ken Waldichuk, really did a great job tonight.

“For Ken, tonight was a night where he threw strikes, pounded the zone, mixed speeds in the zone with his changeup, with his sweeper and had enough [velocity] on the fastball to just keep them off-balance. [His] 67 pitches in six innings shows you that you don’t have to strike guys out. You can get some early contact outs and be successful.”

Waldichuk, following Miller, induced loads of weak contact -- including only one ball in play over 90.4 mph. Over his past seven outings, the 25-year-old rookie has a 2.63 ERA, largely due to a new-look gameplan that features his changeup more heavily.

Against a lineup that entered Monday with the second-best OPS vs. left-handers in the Majors, Waldichuk used the changeup to perfection, inducing six swings-and-misses to pair with his sweeper.

“That’s probably the best I’ve commanded [the changeup],” Waldichuk said. “In past outings, especially when I walk more guys, that changeup kind of gets me in trouble when I spray it. So having that tonight was pretty big.”

Miller, making his second outing since returning from a mild ulnar collateral ligament sprain in his right elbow, needed 30 pitches to labor through the first inning. But he worked around a Jeremy Peña single and a walk to Yordan Alvarez, regaining his command for five consecutive outs (three strikeouts) to finish near his pitch limit with 45 pitches (28 strikes).

In his first outing back (two perfect relief innings vs. the Blue Jays on Sept. 6), Miller said he felt “rusty,” but the right-hander with dominating stuff said he felt more comfortable on the mound this time out. The A's top pitching prospect, per MLB Pipeline, averaged 99.5 mph on his fastball on Monday, and perhaps most importantly, his arm felt “awesome” after the start.

“[Miller] might be one of the best arms I’ve ever seen in person, if we’re being honest,” Waldichuk said. “His stuff is just unreal. It’s fun to watch him out there, and I knew when he was opening today, I was like, ‘He’s going to set the tone.’”

The plan for Miller going forward is for him to continue as an opener to build his workload this season before stretching him out into a starter for next season, Kotsay said.

The opener strategy helped Waldichuk, who has found success with “soft landings,” as Kotsay called them. It also led to Monday’s shutout, in a perfect example of how high the ceiling can go for Oakland’s rotation.

The combination of the two rookies with bright futures, along with Trevor May’s scoreless ninth, shut down an Astros’ lineup that had scored 60 runs and hit 18 homers in its previous six games.

“The first guy, really, I don’t think we had ever seen him, and he was throwing 100,” Astros manager Dusty Baker said. “They switched to a guy that was completely the opposite. Sometimes that opener works. Waldichuk, he was changing speeds -- high fastball, a lot of changeups.

“They threw a good game against us. It doesn't matter who you’re playing if a guy is dealing on the mound out there. And that’s what they were doing. They pitched a hell of a game against us.”