BALTIMORE (AP) -- For a change, everything went swimmingly for the Houston Astros. Their starting pitcher was sharp, the offense had three home runs among its 14 hits and the game was essentially decided in Houston's favor by the end of the fourth inning. It all added up to an 11-0 win over the Baltimore Orioles on Wednesday night. Rookie left-hander Brett Oberholtzer allowed three hits over seven innings to earn his first major league win and Jason Castro hit a grand slam to provide the Astros with their most lopsided victory of the year. Afterward, manager Bo Porter found himself in the rare position of categorizing all the highlights from a gem of a game from the team with the worst record in the majors. ''It all started on the mound with Oberholtzer,'' Porter said. ''What a tremendous job. It's amazing what happens when you throw strikes and don't put people on base. He did a great job of attacking the strike zone.'' Oberholtzer (1-0) was thrust into the starter's role after Erik Bedard was scratched with a sore shoulder. Making his fourth appearance and first start in the big leagues, Oberholtzer struck out six, walked none and did not let a runner get past first base. ''Everything was on today, worked good,'' he said. ''Whenever someone calls on me to come in and get outs, that's what I do - whether it's relief or starting.'' Porter said, ''You certainly don't expect what we ended up getting, but to his credit he did a tremendous job attacking the strike zone against a really good hitting lineup.'' Matt Dominguez homered and had a career-high four hits for the Astros, who built an early 9-0 lead against Miguel Gonzalez (8-5). ''Offensively, those guys kept a lot of pressure on the other team and gave us a little cushion,'' Porter said. Hours before the first pitch, the Astros traded right-hander Bud Norris to the Orioles for outfielder L.J. Hoes and a minor league prospect. Hoes switched from the Baltimore starting lineup to batting second for Houston and went 0 for 5. Norris, the focal point of the trade, will start the deciding game of the series Thursday night against his former teammates. This was the second time in three games that the Orioles were shut out. Before that, they were blanked in three of 105 games. ''We haven't swung the bats real well as of late,'' manager Buck Showalter acknowledged. ''Kind of collectively. You don't say that's just one of those things that's going to happen. You want to shorten it up and get back to what we're capable of. Tomorrow's an opportunity to do that.'' Baltimore finished with seven hits, two apiece in the eighth and ninth innings. Gonzalez yielded a career-high nine runs, four earned, in 3 2-3 innings. He has lost two straight decisions for the first time in 34 career starts. ''My bullpen was great. Everything was down, and I thought I was going to go out there and do pretty well,'' the right-hander said. ''The first inning was good, second inning I was just leaving the ball up, and it just carried on throughout the whole game. It was just a tough night for me overall.'' Houston took control with a four-run second. After Castro hit a leadoff double, Brandon Barnes delivered an RBI double and scored on a single by Dominguez before Robbie Grossman hit a shot onto Eutaw Street beyond the right-field scoreboard. The Astros tacked on five runs in the fourth, courtesy of a botched grounder by shortstop J.J. Hardy. The two-out miscue with the bases loaded allowed a run to score, and Castro followed with his first career grand slam. Brett Wallace hit an RBI single in the sixth and Dominguez homered off Francisco Rodriguez leading off the seventh. Grossman, Oberholtzer and reliever Chai-Hen Lo, who made his debut in the eighth inning, all played together in the minors and are now trying to take their game to the next level. ''I'm happy for Obi, he pitched great. I'm happy for Lo to get in a game,'' Grossman said. ''I started with a lot of these guys in Triple-A and it's awesome to see them come up here and have success.'' NOTES: It was the most lopsided defeat of the season for the Orioles. ... Houston CF Brandon Barnes left with lower back tightness. ... The Orioles put RHP Jason Hammel (strained flexor muscle) on the 15-day disabled list and activated Steve Pearce from the DL. ... Orioles star Chris Davis extended his club-record run of games with a strikeout to 24. ... Porter said Bedard was scratched ''to give him a couple extra days of rest.''