Britton, a promising left-hander, allowed one run and three hits over six innings to pick up the win as the Orioles completed a sweep of the Tampa Bay Rays witha 5-1 victory.
"I was really excited," Britton said. "After that first inning, I started to get a lot more comfortable out on the mound."
Britton is filling in for left-hander Brian Matusz, who will miss three to six weeks with muscle soreness on the left side of his upper back. An MRI exam Friday found a strain in a muscle between the ribs and the back.
Matusz was placed on the 15-day disabled list, retroactive to March 30.
Britton, 23, went 3-0 with a 1.35 ERA in five games, including four starts, during spring training.
"He was good," Baltimore manager Buck Showalter said. "He's got a chance to be better."
Also, outfielder Luke Scott is day to day with a strained right groin. He was hurt running out a grounder in Saturday night's 3-1 win over the Rays.
Information from The Associated Press was used in this report.