McLouth blew a bubble with his gum as he rounded the bases. Over his last 10 games, the Orioles' leadoff man is hitting .485 and has scored 14 runs.
Matt Wieters added a two-run double in the first and Chris Dickerson had his first two RBIs of the season with a two-run single in the sixth inning.
Jason Hammel (4-1) pitched into the sixth. A high pitch count ended his night despite a 6-0 lead.
For the second straight season, Hammel has been outstanding in the opening month. In April 2012, he went 3-1 with a 1.97 ERA.
Hammel failed to pitch at least six innings for the first time this season, mostly because his pitch count topped 100 after giving up three hits to open the sixth.
Hammel allowed seven hits and two earned runs. He struck out five and walked three.
Baltimore didn't stop after McLouth's homer. Manny Machado followed with a double and scored after a pair of wild pitches by Maurer, both of which were sliders in the dirt that bounced away from catcher Kelly Shoppach and went to the backstop. Nick Markakis singled and Chris Davis walked before Wieters capped Baltimore's big first inning.
The Orioles tacked on two more in the sixth and another in the seventh.
J.J. Hardy singled with one out in the sixth and Ryan Flaherty followed with a drive to the wall in right-center that Michael Saunders couldn't handle as he leaped on the warning track. Flaherty was credited with a double and both runners scored on Dickerson's blooper over the drawn-in infield.
Baltimore added another in the seventh on Hardy's single.
The first two starts of Maurer's career were highlighted by struggles in the first inning. In his first home start against Houston, Maurer didn't make it out of the first inning, giving up six runs on seven hits and recording just two outs.
Maurer (2-4) was headed down a similar path against the Orioles. Five of the first six batters reached base, prompting Blake Beavan to start warming up in the bullpen with just one out. Maurer got the final two outs of the first, but was done after four innings, giving up four runs on six hits.
Michael Morse opened the Seattle sixth with an opposite-field home run, his eighth of the season and second in three games. The Mariners then got consecutive singles from Jason Bay and Justin Smoak to chase Hammel, and Dustin Ackley greeted reliever Tommy Hunter with a third straight hit to load the bases.
Shoppach hit a weak grounder that scored Bay, but Ackley was forced out at second. Hunter then shattered Brendan Ryan's bat to start a double play that ended the inning with little damage.
NOTES: Machado extended his hitting streak to nine games, tied for the longest by an Orioles player younger than 21. ... Seattle signed veteran OF Corey Patterson to a minor league contract on Tuesday and will send him to extended spring training in Arizona. ... Baltimore optioned LHP Zach Britton to Triple-A Norfolk on Tuesday. Britton was the losing pitcher in his season debut on Monday night.