"I think the past month has been a lot better," Alonso said. "The younger guys, especially myself, are more comfortable. You're seeing it from the younger guys, we're having better at-bats. If you have a group of guys having good at-bats against a pitcher, anytime you do that, it just gets better and better."
Ohlendorf (3-0) allowed two runs, one earned, in his longest outing of the season and gave up six hits while striking out six and walking one. The right-hander has also made four relief appearances but got his first win as a starter this season.
"In the beginning my slider wasn't as good as it was later in the game," Ohlendorf said. "I was really happy with the way I pitched, especially going deeper in the game."
Three relievers combined to hold Houston scoreless and give San Diego its third win in four games.
Maybin drove a ball to the left-center field wall in in the eighth that was caught by a fan who reached over the fence. Umpires reviewed the play and ruled it a double. Two runs scored on the play.
"I saw the catch and I knew it was going to be ruled a double," Padres manager Bud Black said. "I saw it live, but I haven't seen the replay yet."
San Diego strung together four consecutive hits against Houston starter Jordan Lyles in the fifth to build a 4-2 advantage. Chase Headley doubled home Logan Forsythe, and Yasmani Grandal had a run-scoring single.
Amarista's single in the sixth scored Maybin and pushed the lead to 5-2.
Lyles (2-6) yielded five runs on 11 hits over six innings and has yet to win a game on the road in his career. The right-hander walked two and struck out three.
"I didn't make pitches," Lyles said. "I need to just attack each game like it's a new game, put everything behind you. I've just got to get a little more consistent."
Alonso sent a 2-0 pitch from Lyles a few rows deep in the left-field stands in the second to put San Diego on top 2-1. The homer was Alonso's fourth of the season, but his first at Petco Park.
"It only took what, three months?" Alonso said. "Hopefully I don't go that long without one, but that's really not what I'm looking to do. My thing is more doubles and driving guys in, but if it comes, so be it."
Fernando Abad hit Headley with a pitch in the seventh before Alonso doubled to left-center to score Headley and give San Diego a 6-2 lead.
Padres pitcher/pinch hitter Micah Owings will have surgery on his right elbow. Black said the procedure will remove some "loose bodies" from the area. Owings has been on the disabled list since April 26 with a strained right forearm. ... Astros SS Jed Lowrie has a sprained right ankle and a nerve issue in his right leg, according to Mills. Lowrie, on the disabled list since July 15, will wear a boot to immobilize the ankle. ... Astros C Jason Castro has swelling in his right knee but may return to the team when he is eligible to come off the disabled list on Monday.