Guthrie allowed three hits over three scoreless innings in his first spring training start, leading the Baltimore Orioles to a 4-2 victory.
Guthrie will leave Sunday to join the United States squad. Before departing, the right-hander put on a show against Florida that validated his place on Team USA.
"That's why he made the club," Orioles manager Dave Trembley said. "He made the club because everybody knows about him. We wish him well, and hopefully he'll do very good."
Guthrie started for the Orioles on opening day last year and is expected to receive the same assignment this year. There are still five weeks left until the season starts, but Guthrie treated his assignment against the Marlins with midseason intensity.
"Every time I go out there I'm attacking with the best stuff I have, working as hard as I can to get them out," he said.
Guthrie is next expected to pitch for Team USA on March 5, in an exhibition game against the Philadelphia Phillies.
"In my mind I feel it will be similar," Guthrie said. "Just a different uniform."
Against Florida, Guthrie gave up a single in each of his three innings and walked one.
"I felt all right," he said. "My off-speed pitches were really good, and I threw some sliders in the last inning that I felt I had good release on them."
But Guthrie wasn't pleased with his fastball, so he polished up the pitch in the bullpen before running in the outfield.
"I wanted locate four or five fastballs low and away on the outside part of the plate, which I didn't do very consistently in the game," he said. "All of them were right where I wanted, so it was nice to be able to finish on that note."
Aubrey Huff went 3-for-3 with three RBIs for the Orioles, and Melvin Mora drove in a run with a double. Mora and shortstop Cesar Izturis also will be leaving Baltimore to play for Venezuela in the WBC.