Austin Jackson had two hits for Detroit, which scored its five runs in the fourth inning.
Feldman signed a three-year, $30 million contract with the Astros in the offseason, and Houston hopes the 31-year-old right-hander can provide stability at the top of the rotation. Feldman went 12-12 with a 3.86 ERA last year while splitting time between the Chicago Cubs and Baltimore Orioles.
"He was Scott Feldman. He's going to attack the strike zone, he's going to throw all his pitches in any count," Astros manager Bo Porter said. "Just a professional, the way he goes about his business, and it was good to see."
Feldman allowed a walk to Miguel Cabrera and a single to Jackson.
"Right now I think the pitchers are probably a little ahead of the hitters, and all that stuff catches up," Feldman said. "Hopefully by the end of spring I'll be able to hit my spots."
Cabrera's single started Detroit's fourth-inning rally, which also included a two-run double by Don Kelly.
Tigers: Left-hander Kyle Lobstein was only supposed to pitch two innings, but he breezed through them with such ease manager Brad Ausmus let him pitch one more. A third-inning walk was the only baserunner Lobstein allowed. Barring injury, there's no room for him in Detroit's rotation, but he made a strong impression.
"He's in that mix of guys that could fill in," Ausmus said. "He's got good mound presence. He doesn't look like he's nervous out there, he doesn't look intimidated."
Astros: Feldman pitched fine, but it was a rough day for another potential starter. Brad Peacock pitched a hitless third before allowing five runs without retiring a batter in the fourth.
Jackson has been Detroit's leadoff hitter during the Tigers' run of three straight AL Central titles, but he may end up elsewhere in the lineup this season after Detroit acquired Ian Kinsler in a trade and signed speedy outfielder Rajai Davis.
Jackson hit sixth Saturday, and he came up with the bases loaded in the fourth after singles by Cabrera and Victor Martinez and a walk by Alex Avila. Jackson's single to center opened the scoring, and Kelly followed with his double to make it 3-0.
"You have to make the adjustment," Jackson said. "Leadoff, there's a different approach. Your job I think is to make sure you're doing whatever you can to get on base. Down the lineup, you have more opportunities to hit with runners on."
Carlos Correa, the No. 1 pick in the 2012 draft, entered the game at shortstop in the fifth for Houston. He doubled to start the sixth and eventually scored the Astros' lone run of the game.
George Springer, another top Houston prospect, started in center field and hit a fifth-inning single.
CLOSING IT OUT
Closer Joe Nathan didn't pitch for the Tigers, but they did use three relievers who are expected to play key roles in the bullpen this year. Al Alburquerque walked one and struck out two in the seventh, and Ian Krol allowed a walk and a single but kept Houston from scoring in the eighth.
Bruce Rondon pitched a perfect ninth.