Matusz, who admitted the time away felt like "it'd been forever," shook off some early nerves and was encouraged with his stamina throughout the outing, although his command left much to be desired.
"That's the one thing that killed me today was getting behind at times," said Matusz, who was charged with six runs on eight hits and three walks -- although two of those runs came after his 109-pitch outing was through.
"I've made a lot of strides, had a good feel for all my pitches today, just being able to locate a little bit better. And keep going out there, getting the experience and getting the confidence and a better feel for being out there."
After a rocky start to the night -- in which he issued three walks and allowed three runs in the first 1 1/3 innings -- Matusz settled down considerably, holding the A's in check with a fastball that spent most of the evening in the 88-90 mph range.
"We had him on the ropes," Oakland's manager Bob Melvin said. "Early on, you wouldn't have thought he'd be out there in the seventh inning. In the middle innings he got better and mixed his pitches better and allowed them not to have to use their bullpen so much. He was able to clean it up and pitch better."
"His fastball was back to having life, to where he should have the pitches to have the success at this level," added catcher Matt Wieters.
Matusz (1-5, 8.63 ERA), who continues to work his way back to the form that had him projected as the team's No. 2 starter coming out of camp, was backed Tuesday night by a pair of impressive outfield assists from Adam Jones, who saved a run with an inning-ending catch and throw home in the second before erasing a leadoff single from Josh Willingham in the sixth.
Jones -- who entered the game already leading all Major League center fielders in assists -- caught Brandon Allen's fly ball and fired it to first base to get Willingham and pick up his 14th assist of the season.
With Tuesday's pair of putouts, Jones is now second among outfielders in assists, trailing only Kansas City's Alex Gordon.
No. 9 batter Josh Bell, who figures to get more playing time with Chris Davis on the DL, drove in two runs, while Vladimir Guerrero doubled in Jones for a run in the fourth.
That was all the O's could muster off A's starter Guillermo Moscoso, who went six strong innings en route to his sixth victory this season.
Orioles relievers Troy Patton and Chris Jakubauskas were each charged with a run, with Patton also surrendering a two-run double to Coco Crisp, though both runs were charged to Matusz.