Feldman was pulled with one out in the sixth following a season-high 117 pitches, leaving with a pair of runners on base. Within a matter of minutes, the A's blew the game wide open with a Brandon Moss grand slam and cruised to a 13-1 win in the series finale.
"They've got a tough lineup, tough team," Feldman said. "They do things the right way and play the game right, and there's a reason they're so good. Obviously, I didn't help myself by walking five guys. You can't do that against those guys. They're good enough when you're not walking them that they still make you work. It's frustrating to walk that many guys."
The 13 runs allowed by the Astros tied a season high, and the margin of defeat was their largest of the season. The A's didn't chase many pitches out of the zone, but it didn't help that Feldman was putting them in some counts to be a little more selective.
"That's their motto," Astros manager Bo Porter said. "It's a lot of deep counts. He battled, but at the same time, they did a tremendous job of hitting with men in scoring position, and that pretty much was the difference in the ballgame."
Feldman (4-8) lost his third consecutive start after allowing six runs, nine hits and walking five (one intentional) in 5 1/3 innings. He's won only twice since beginning the season with two terrific outings in early April, and is 1-6 with an 8.73 ERA in seven career starts in Oakland.
"I would not have expected that," he said of his struggles. "Hopefully, we can keep grinding and pitch better. I've got to pitch better. It can be a frustrating game at times, but try to stay on the grind and figure it out."
The A's were 6-for-15 with runners in scoring position and saw 22 men reach base following a 1-2-3 first inning by Feldman.
"We had baserunners out there all the time, which was a little bit more pressure on the starting pitcher," A's manager Bob Melvin said. "It took us a little while to actually cash in on a lot of them, but you know if you continue to put guys on base that you're going to come through. The approach was real good. When we're going about our game, when we're doing well, that's kind of the approach we have."
With the Astros trailing, 4-1, in the sixth, Anthony Bass replaced Feldman and hit Josh Donaldson with his second pitch to load the bases for Moss, who sent the next pitch soaring over the right-field wall for a grand slam, his third of the season, that made it 8-1. Oakland scored four more in the eighth off Josh Zeid.
"Our bullpen, they couldn't keep it there," Porter said. "In that situation, you turn to the bullpen with hopes of trying to keep it close. We were unable to do that with the guys that we brought into the game."
Samardzija, the All-Star acquired from the Cubs three weeks ago, dominated the Astros for eight innings. The only run the Astros managed came on a one-out home run in the fourth by Chris Carter, who tied George Springer for the team lead with 20. Carter's seventh homer of July dinged off the left-field foul pole.
"The reason they went out and got Samardzija is because he gives them games like he gave them today," Porter said. "You're talking about a front-of-the-rotation guy that gave them eight strong innings and pretty much had complete command of the game. And offensively, they did what they've pretty much done the entire season -- they make you work and make you throw strikes, and they were able to get the big hits once they got men in scoring position."