One day after arriving in a trade from Philadelphia, Happ allowed two hits over six innings in his Houston debut and the Astros beat the Milwaukee Brewers 5-0.
Happ and two minor leaguers came to the Astros on Thursday in a trade that sent Roy Oswalt to Philadelphia. Oswalt allowed four earned runs and seven hits in six innings in the Phillies' 8-1 loss at Washington on Friday night.
Happ looked more like the seasoned veteran.
"It's a strange thing to fly out this morning, meet the new teammates and then go out there and pitch but it was good," Happ said.
"It was very emotional yesterday [Thursday] saying goodbye to the guys I've played with a few years and then coming in here and meeting new guys."
The Brewers have lost three straight after winning their previous five games. The Astros won their third straight.
Happ, 12-5 as a rookie last season, made only his fourth major league start this year. He was sidelined with a left forearm strain. He had four walks and six strikeouts as the Astros combined on a four-hitter and their fifth shutout this season.
Milwaukee manager Ken Macha liked the Astros' newest starter.
"He has good stuff," Macha said. "He throws 93, has a good hard slider. I knew that coming in. He mixes in a couple curveballs, a couple changeups. I said pregame that I voted him for Rookie of the Year last year. He has a good arm."
All the Astros' runs came on homers. Jason Michaels hit a solo shot in the second, and Chris Johnson added a three-run homer in the fourth. Johnson extended his career-best hitting streak to 13 games.
"We got a pretty good pitcher, he was real good tonight," Johnson said. "We got him a little lead so he could relax. I'm sure he had some nerves at the start but he was pretty nasty tonight."
Happ started his Astros career by yielding a double to Rickie Weeks and then he walked Corey Hart. He then retired the side and didn't allow another hit until Casey McGehee's one-out single to left in the sixth inning.
Manny Parra (3-8) went 5 1/3 innings for Milwaukee. He allowed four hits, walked three and struck out six.
"I threw the ball really well," Parra said. "It is what it is. It's baseball. Their job is to hit the ball."
Johnson went 2 for 3 and is hitting .417 in his streak.
Happ left two runners stranded in the fourth. McGehee reached on Carlos Lee's fielding error and after Jonathan Lucroy flied out, Carlos Gomez walked. Happ then got Alcides Escobar on a fly ball and Parra grounded out.
Macha wasn't critical of his starting pitcher.
"Their guy [Johnson] hit the ball in the right-center field gap for a homer," Macha said. "I thought Manny pitched pretty well. Just little things add up."
Astros SS Tommy Manzella, on the DL since June 24 with a fractured left index finger, has been taking ground balls. ... Prince Fielder of the Brewers needs one RBI to reach 500 for his career. ... Johnson's 13-game hitting streak is the longest by an Astro since Julio Lugo hit in 14 straight in 2000. ... RHP LaTroy Hawkins has been reinstated from the 60-day DL. He had right shoulder weakness. ... Weeks is attempting to become the second player in major league history to drive in at least 100 runs batting leadoff. He has 67 RBIs and is on pace for 105 this season.