"If we could have kept the game right there, an opportunity to come back up in the ninth inning with a one-run deficit is totally different than coming up down by six," Porter said. "The whole object was trying to keep the game right there."
Oakland starter Jeff Samardzija held the Astros to two runs and six hits and struck out 10 batters in eight innings to improve to 2-0 with a 2.78 ERA in three starts against the Astros since coming to the A's in July.
"I tell you what, he had it all working tonight," Porter said. "He was plus and minus-ing his fastball, anywhere from 91 to 96 [mph], and pretty much was in complete command of the game until Carter hit the two-run homer."
Samardzija (6-10) was coming off a rocky outing in which he allowed seven runs and seven hits in 3 2/3 innings against the Mets.
"I felt like it got away from me my last start, so I wanted to come out and really go pitch to pitch and hitter to hitter and not really look at it as a whole and break it down as something I could control, not letting previous things affect the future things," he said.
Samardzija was four outs away from shutting out the Astros when Carter belted a two-run home run to right field on an 0-2 pitch -- his 31st of the season -- to cut the lead to 3-2. Thirteen of Carter's 31 homers have come with two strikes, which is the most by an Astros player since Lance Berkman had 18 in 2006.
"All game he was throwing me fastballs away and I was missing them and I finally hit one on the barrel," Carter said.
Sipp began the ninth by walking four consecutive batters on 23 pitches, forcing in a run when he walked Coco Crisp. Jose Veras replaced him and gave up a two-run double to Josh Donaldson and a two-run single by Derek Norris, though all but one run was charged to Sipp.
"Tony Sipp's been good the whole year," Porter said. "It's one of those things he pretty much lost command, and obviously those guys were patient enough and were able to wait it out and take the walks that were given to them."
The Astros, who heading into the weekend were leading the American League in runs scored since the All-Star break, have fallen on hard times offensively. They're hitting .165 in their last five games, during which they're 1-4.
"It's a funk," Porter said. "I believe in these guys in that clubhouse and I believe we're going to be able to pull out it."
Astros starter Scott Feldman (7-10) delivered his fifth quality start in his past six outings by holding the A's to three runs and seven hits in seven innings in a losing effort. His 15 quality starts this season rank second on the club behind Dallas Keuchel.
Feldman got in trouble when he allowed a leadoff double to Eric Sogard in the third inning. He was caught in a rundown between second and third and tagged out, allowing Alberto Callaspo to sneak into second with a fielder's choice. He scored on a Donaldson double.
In the fourth, Josh Reddick followed a one-out single by Brandon Moss with his 10th homer, a two-run shot to right field that made it 3-0. That's his third homer against the Astros this year.
"For the most part I was making my pitches all night and thought I had pretty good command," Feldman said. "I just really missed my spot bad to Reddick there and he's been seeing the ball pretty well off of me this season. He wasn't going to miss that mistake."