Gregerson, who recently had a 110-batter stretch without allowing a walk end, walked two consecutive batters with two outs in the 10th inning before giving up Michael Bourn's two-run triple in Houston's 6-3 win over the San Diego Padres on Thursday night.
Gregerson, the club's seventh-inning set up man for closer Heath Bell, has been an instrumental part of the majors' top bullpen that has played a big role in San Diego's run to the top of the NL West.
But against the Astros, Gregerson hit a wild patch that proved decisive.
"I couldn't find the zone," he said. "That's pretty much it. I was having a hard time with my slider. I couldn't get it over or my fastball, either."
Gregerson (2-3) came into the game having walked just four batters in 39 1/3 innings.
"That was another one that I tried to get down, and it didn't get down," Gregerson said about Bourn's triple.
Gregerson's streak without a walk lasted from April 14 to June 18. The streak was the longest for a reliever in San Diego's history and the longest in the majors since Boston's Jonathan Papelbon went 127 straight batters without a walk in 2008.
"Their bullpen has been great for them this year," said Houston's Jason Michaels, who had a solo homer. "Guys had some great at-bats and were able to get on base. That's a huge hit there for Bourn."
In the four innings preceding Gregerson, San Diego's bullpen had allowed just one hit with an intentional walk and three strikeouts as the Padres came back from a 3-0 deficit. San Diego came into Thursday's game with the lowest bullpen ERA in the majors at 2.73.
"Taking it late in the game tied, you like your chances," San Diego manager Bud Black said. "It just didn't happen."
"It was nice to see those good at-bats in the crucial part of the game," Astros manager Brad Mills said.
It was Houston's sixth win in nine games after having dropped nine of 10. San Diego has lost three of four.
Five of Houston's six runs were scored with two outs.
The Astros took a 3-0 lead in the second inning but San Diego chipped away for one run in the fifth and two in the seventh, tying it on David Eckstein's RBI single.
Hundley scored the Padres' run in the fifth. He walked with one out and advanced to second on a groundout. Pinch-hitter Chris Denorfia drove Hundley in with a single to right field.
Brian Moehler pitched effectively into the sixth inning for Houston, limiting San Diego to one run and four hits a day after the Padres had 14 hits in a 13-3 win over Colorado.
Michaels hit his fifth home run leading off the second inning against Jon Garland to give the Astros a 1-0 lead.
After consecutive walks, Garland retired the next two batters before intentionally walking Bourn to load the bases. Keppinger then capped off the inning with a two-run single.
The Astros had Garland in constant trouble throughout his five innings. Houston had base runners in each inning, but stranded nine against Garland.
San Diego's Chase Headley went 3 for 4 with a pair of doubles.
Garland, who had won two straights starts, allowed three runs and six hits. The right-hander walked a season-high six and struck out three.
Padres LF Scott Hairston was ejected in the eight inning by home plate Ron Kulpa after he was called out on strikes. ... In three career appearances at Petco Park, Moehler is 2-0 with a 2.36 ERA. ... There was a moment of silence before the game for former San Diego Chargers and San Diego State coach Don Coryell, who passed away Thursday. ... Smoke from a fire was visible in the downtown skyline a few blocks beyond center field. An earthquake rocked Petco Park on June 14 during a game against the Toronto Blue Jays.