Cincinnati Reds second baseman Brandon Phillips was ejected in the eighth inning for arguing a checked-swing third strike.
His replacement, Wilson Valdez, let a potential victory slip right under his glove as the Houston Astros edged the Reds, 2-1, in the middle test of a three-game set.
Pinch-hitting for Fernando Martinez in the ninth inning, Matt Downs banged a two-out double off the wall in left field off Sean Marshall (4-5) before Matt Dominguez was intentionally walked and pinch-hitter Brandon Barnes was hit by a pitch to load the bases.
Jose Altuve then hit a slow roller to second, but it got by Valdez, and Downs came home for the winning run.
"That's every ballplayer's nightmare right there," Reds manager Dusty Baker said of the error. "Wilson is a very sure-handed fielder."
Wilton Lopez (6-3) picked up the win after getting the final two outs in the top of the ninth for Houston, which snapped a six-game skid.
Prior to the final frame, Reds starter Homer Bailey and the Astros' Lucas Harrell engaged in a pitchers' duel. Bailey fanned nine and surrendered a run on three hits and one walk over eight innings, while Harrell allowed a run on seven hits and a walk in seven frames.
The Reds struck first with a run in the opening inning. Zack Cozart led off the game with a single to center and Drew Stubbs reached on an infield single to put runners on first and second. Cozart scampered to third when Phillips grounded into a fielder's choice, and scored on Ryan Ludwick's sacrifice fly to left field.
Houston, which had just one hit through the first three frames, tied the contest in the fourth when Justin Maxwell sliced an opposite-field homer over the wall in right field.
"I'm really excited what's going to happen here the next month," Astros interim manager Tony DeFrancesco said. "We've got a nice group of guys that's trying to compete, trying to establish themselves. It's going to take a little time and a little patience."
Maxwell has hit seven of his 13 homers when Harrell is pitching ... Phillips had his 10-game hitting streak snapped ... Harrell has allowed two runs or less in 11 of his last 13 starts. He leads all NL rookies in innings pitched (165 1/3) ... The NL Central leaders had their four-game winning streak snapped.