Matusz pitched four hitless innings, struck out six of his first seven batters and retired his first 11 before a walk in Wednesday night's 9-4 win over the Minnesota Twins.
"My mindset was to attack the zone with authority and come out there and just play the game and pitch," Matsuz said. "Just build enough confidence. Just keep building, building and stay strong all the way through."
Matusz had a 10.69 ERA in 2011, the highest in a season for a pitcher with at least 10 starts. He was 5-10 with a 5.42 ERA in 16 starts last year, then was sent to the minors on July 1 after losing his fifth straight outing.
Baltimore brought him back on Aug. 24, and he was 1-0 with a 1.35 ERA in 18 relief outings, holding opponents to a .114 batting average.
Baltimore right fielder Nick Markakis returned to the team after an MRI in Baltimore showed he has a small herniated disk in his neck and will be out about another week.
"I'm confident that I'm going to be OK," said Markakis, who hopes to be able to play in three-to-four consecutive exhibition games. "Whether I'm there opening day or not, it depends on how my body reacts and how I feel."
Minnesota's Justin Morneau went 0 for 3 with two strikeouts in his first game back after playing for Canada in the World Baseball Classic.
"He's one of the best hitters in the league for a reason," Matusz said. "He just keeps fighting. I felt like I was making good pitches. He was just putting good swings on it. That last pitch, I just said, I'm going to bury a slider here.' He's such a good hitter, he still put good wood on it. With those tough hitters, you've just got to bear down and throw strikes."
Morneau said he benefited from playing in the WBC.
"It was something I'll never forget," he said.
"We've got all kinds of guys who can play third," Twins general manager Terry Ryan said. "It's just a matter of how much offense we'll get."
Twins minor league RHP Deolis Guerra remains in Tampa in intensive care for a blood clot in his pitching shoulder. He is expected to have surgery within a few days. "This was precautionary," Ryan said. "This is something that a lot of people have had. We've had four guys ourselves. A blood clot is certainly a serious situation. But I believe he'll be back in time." Ryan said he had no doubt Guerra would pitch again this season. ... Twins LHP Scott Diamond, who had offseason surgery to remove bone chips from his elbow, remains slated to pitch in a game Monday.