"Obviously, we all want Roy starting that game, because he's the ace of the staff," Moehler said. "It's just unfortunate that he's injured right now."
Moehler will be followed in the rotation by Wandy Rodriguez and Brandon Backe in a three-game series with the Chicago Cubs.
Starting July 21, when the Pirates visit Houston, the rotation becomes less certain. The fourth spot will likely go to Runelvys Hernandez, who would be called up from Triple-A Round Rock to fill the spot.
The final spot is still being earmarked for Oswalt, who left Friday's game in the first inning with a strained left hip abductor. No decision is expected until at least Friday on whether Oswalt will pitch, rest, or head to the disabled list.
"He won't do any throwing until after the break," manager Cecil Cooper said. "There's no need."
Cooper praised Moehler on earning the top spot, saying that the 36-year-old pitcher had been a huge boost to the team this season. Moehler signed a one-year contract with the Astros in January, then earned a spot in the rotation after starting the season with a string of six solid outings.
"He took the ball, stepped into that role, and gave us quality start after quality start," Cooper said. "We really needed that."
The right-handed pitcher, who relies on his control, currently has a 5-4 record with a 4.28 ERA. Most importantly, he's provided a consistent presence all season long.
In his most recent outing, Moehler went six innings and allowed four runs as the Astros defeated the Pirates on Wednesday. He said his main goal is to help the team stay competitive in the second half.
"I've had some games I'm pleased with, and some I'm not, but I'm happy with the way things are going," he said. "Obviously, I'd like to see our record be a little better, but we have a chance to finish well."
Cooper said that Moehler's season has been a success by every measurement.
"I hate to think where we'd be without him," the manager said. "He's been about as consistent as you can ask."
Michael Phillips is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.