"It's hard coming in every day and getting beat," said third baseman Chris Johnson, who went 2-for-4 with a homer. "Guys are getting [ticked] off a little bit and want to come out here and get a win."
Marte, who arrived from Triple-A earlier in the day, clubbed the first pitch of the game over the wall in left-center to become the 13th player since 2000 to homer on the first pitch thrown to him, and the first Pirates player to homer on his first big league at-bat since Don Leppert on June 18, 1961.
"I was telling the boys before the game in the dugout, if he throws a fastball in the middle, I'm going to take a hack at it," Marte said through interpreter/first-base coach Luis Silverio. "And that's what he did, and that's why I did."
Keuchel says he typically tries to groove a first-pitch fastball and hadn't had anyone take him deep in his Minor League career.
"I figured he would take a strike to see what I've got," he said. "I never thought he was going to hit a home run the first pitch of the game. That's a career-first for me. I tip my cap to him. He put a good swing on it. Just that first inning was rough locating the two-seam, and I was leaving balls up."
Keuchel (1-3) gave up a two-run homer to Garrett Jones later in the first inning, and Clint Barmes hit a two-run shot in the second to give the Pirates a 5-0 lead. The rookie pitcher actually settled in nicely, retiring the next 10 batters and 17 of the final 20 batters he faced.
"I left a few pitches up first inning and that kind of cost me," he said. "I thought after that two-run bomb to Barmes that if I collected my thoughts and got it back together I could get through some innings and ended up settling in and got some ground balls there."
Keuchel pitched six innings and allowed just two singles outside of the home runs, walking a pair of batters. He had walked four batters in four of his previous five Major League starts this year, so the better command was a promising sign.
"I've had a lot of walks and coming into this start I wanted to attack the zone more and make them swing the bat," he said. "I think I did that for the most part. I had two walks, but overall I thought I felt good. First pitch I usually like to throw split down the middle with the two-seam and he got me."
But the Astros' struggling offense -- which has a .216 batting average in the last 25 games -- was held to two singles through seven innings. Pirates starter A.J. Burnett (12-3) carried a two-hit shutout into the eighth to beat the Astros for the first time in three starts this year.
"A.J's had success for the better part of his career so we knew what we were getting into," manager Brad Mills said.
Johnson broke up Burnett's shutout bid with a leadoff homer in the eighth inning. It was his seventh homer of the year and first since June 24. Carlos Corporan homered to right field one out later, chasing Burnett from the game.
"The first two innings were tough, but after that for seven innings our pitchers did pretty well," Johnson said. "They kept us in the ballgame and gave us a chance there at the end with the tying run at the plate. We're going to keep battling back. Just because we get a big deficit doesn't mean we're going to give up."
Houston got a two-out RBI single by Johnson in the ninth to bring the tying run to the plate, but Pirates closer Joel Hanrahan was able to strike out Brian Bogusevic for the final out and secure his 30th save, which is four fewer wins than the Astros.
Mills said the Astros need to make some adjustments offensively. Houston is averaging 2.6 runs per game in 15 games since the All-Star break.
"We need to have those better at-bats and try to move forward," he said. "Later on in the game, we started doing that. We would've liked to have seen that earlier in the game because, like I said, we knew exactly what we were getting into."