Harrell kept his composure in a difficult sixth inning by limiting the damage to two runs and carried the Astros to a 3-2 win over the Atlanta Braves on Saturday night.
"I got away from my strengths and started nibbling a little too much at the end," Harrell said. "It got me in trouble walking guys. I felt like my changeup really bailed me out in a couple of situations."
Justin Maxwell had a career-high four hits, including two homers, Harrell won his first career start at Turner Field, and the Astros snapped a four-game losing streak.
The Astros won for just the fourth time in 33 games, improving to 11-45 on the road -- the worst mark in the majors.
Paul Maholm (9-7) lost his Atlanta debut, allowing three runs, six hits, and two walks. He struck out eight in seven innings.
The Braves had won two straight and nine of 10.
Harrell (9-7) allowed two runs and four hits with five walks and five strikeouts in six innings. In eight starts since losing at Texas on May 16, the right-hander is 3-2 with a 2.26 ERA.
Harrell retired the first two batters he faced in the sixth before walking Chipper Jones, Freddie Freeman and Brian McCann to load the bases. Dan Uggla's two-RBI single to left field tied it at 2, but Harrell ended the threat when Paul Janish grounded out.
"He keeps battling," Astros manager Brad Mills said. "I know he had a rough sixth inning. His command started to leave him a little bit, but we really needed him to get through that sixth inning to set up the bullpen, and he did. He wanted the ball and he wanted to stay in there."
Wilton Lopez got two outs to earn his second career save, and first since 2010. He had converted one of his previous 11 save opportunities.
Lopez, who took over as closer following the trade of Brett Myers and a foot injury to newly acquired Francisco Cordero, relieved Wesley Wright with the bases empty. He walked Uggla before pinch-hitter Juan Francisco grounded into a double play.
Maxwell's two-run shot made it 2-0 in the fourth, and he added his 12th homer leading off the seventh to give Houston a 3-2 lead. It was his first two-homer game since he played for Washington in an 11-3 loss at Florida on Sept. 12, 2009.
"The two home runs were probably the only two mistakes I really made," Maholm said. "The first one was a fastball that ran back over and the second one was a hanging curveball. He did a good job of hitting them a long way."
Maxwell singled in his other two at-bats to go 4-for-4 for the first time in his career. Six of his homers this season have come with Harrell pitching.
"Maybe he thinks I should pitch more often, but it was a great all-around team effort," Harrell said. "I thought everybody played real well. The defense played great. Snyder called a great game for me. I think I only shook off once, but aside from that, it's just a big win for us."
Maholm, acquired Monday from the Chicago Cubs, had a career-high, five-start winning streak snapped. The left-hander came in 12-6 with a 3.11 ERA in 21 previous starts against Houston.
The Astros snapped a six-game losing streak in Atlanta with their first victory there since May 3, 2009.
Fernando Rodriguez faced the minimum in the seventh, and Wright did the same in the eighth for Houston.
Harrell had allowed two hits before Jones led off the fourth with a single and moved to second on Freeman's groundout. After McCann walked, Harrell escaped the jam when Uggla grounded into a double play.
Harrell improved to 3-6 with a 5.71 ERA in 12 starts on the road.
"Any win is a lift," Maxwell said. "We've been struggling all year, but we haven't given up at all. We know we're not in a good situation right now, but if we keep playing hard, it's going to get better for us in the future."
Cordero will visit a doctor in Houston either Tuesday or Wednesday. He was placed on the 15-day disabled list Friday with an inflamed right toe. ... Houston manager Brad Mills said OF Steve Pearce (neck) might return to the lineup on Sunday.