HOUSTON -- Garrett Atkins bent, hands on knees, on the infield dirt, looking isolated after popping out against Astros reliever Chris Sampson with two on and two out in the eighth inning.

Atkins went 0-for-4, with two of the outs coming after the opposition walked Brad Hawpe to get to him -- a show of disrespect. Atkins troubles were one of the factors in a 6-4 loss to the Astros at Minute Maid Park on Wednesday night.

"It's frustrating," Atkins said. "You keep coming here every day thinking today's the day you're gong to turn it around and help your team."

A once-feared RBI man with a .188 batting average is a major problem for the Rockies, whose four-game losing streak includes the first three of the series with the Astros. Atkins isn't alone in struggling at Minute Maid, where the Rockies are 7-24 in the stadium's 10 seasons.

Atkins is not taking advantage of a new chance from Rockies manager Jim Tracy. Clint Hurdle had begun dropping him in the order, playing him sporadically or leaving him out of the lineup because of non-production.

Atkins, who hit fifth Wednesday but has hit cleanup under Tracy, has gone 1-for-11 in this series, which ends Thursday night. He hasn't had more than one hit in a game since going 3-for-4 against the Padres on April 27.

On Wednesday in the sixth inning, after the Astros walked Hawpe to put runners at the corners. Atkins hit a hard bouncer to third, and Clint Barmes was thrown out at the plate. In the eighth, after Todd Helton doubled with two out, Hawpe took another intentional pass and Atkins popped out.

"You're getting to the point where you're going to have step back and ask yourself the question, is it going to happen or not," Tracy said.

There's also the problem of pitcher fielding. The Astros' go-ahead run scored on the 11th error by a Rockies pitcher this season. That matches last year's total and trails only the Cubs, who have 12, in the Majors.

With the score tied, 4-4, in the seventh, Rockies right-hander Joel Peralta forced a Geoff Blum grounder to first baseman Helton that should have ended the inning with a double play. But Peralta, covering first after Helton threw to second, missed Barmes' throw. Carlos Lee scored from third.

The Astros added a run on Hunter Pence's fourth hit -- an RBI single -- off Manuel Corpas in the eighth. Pence also had an RBI single in the first, a triple in the fifth and a home run off Rockies starter Jason Marquis (7-4) in the seventh.

Marquis gave up three runs on five hits, just one of them hard, and a walk in the first inning but, as Tracy said, "did a tremendous job recovering" until Pence's leadoff homer in the seventh. Charged with five runs in six innings, Marquis has given up 14 runs, 13 earned, and 20 hits in 9 2/3 innings in his two starts against the Astros this season.

Pence is 11-for-22 in his career against Marquis.

"I don't know what his numbers are, but he's a pretty good hitter, pretty good player," Marquis said. "He can hurt you when you make mistakes."

The Rockies' Ian Stewart knocked a three-run homer off Astros starter Brian Moehler in the fifth. Stewart, whose homer was his eighth of the season, has homered for all four of his hits against the Astros this year. He has a solo shot, two- and three-run homers and a grand slam.

"It was supposed to be away, but it was down the middle and it got too much of the plate," Moehler said. "He's got that uppercut swing and got every bit of it."

Helton's sacrifice fly in the sixth ended the Rockies scoring, giving them a 4-3 lead. The Rockies put two on in the ninth, but Sampson (third save) escaped. Michael Bourn's run to deep center to catch a Ryan Spilborghs fly ball saved the Astros.