Penn took the place of Erik Bedard, who went on the disabled list Thursday with a strained left knee ligament, and he proved why he is one of the O's top prospects.
After allowing a home run to Craig Monroe on a 3-2 pitch in the second, Penn came back and retired the next six Tigers. He struck out two of those batters and four in the game. Mazzilli said the pitch before Monroe's home run could have been called strike three.
In the fourth, Penn displayed a level of concentration far beyond his years when he recognized that first baseman Rafael Palmeiro went after a Jason Smith ground ball with the bases loaded. Penn hustled off the mound and received the throw from Brian Roberts at first to end the threat.
Penn did not earn a decision in his first start. He allowed three runs, but two were unearned.
The right-hander was halfway to the dugout thinking he had just escaped another bases-loaded jam in the fifth, when Palmeiro dropped Miguel Tejada's throw to first on what should have been a double-play.
Penn stopped in his tracks, showing frustration for a moment but walked back to the mound calmly to resume his business. Like a wily, media-savvy veteran, he deflected any blame that could have been placed on his teammate.
"My defense wasn't on its toes all the time because I was throwing balls," said Penn, who appeared comfortable surrounded a horde of reporters after the game. "I've got to throw strikes and keep them in the game."
Penn's biggest obstacle was his control. He walked four batters, and 48 of his 101 pitches were out of the strike zone.
"He showed that he has a pretty good fastball and that he can locate it at times," catcher Sal Fasano said. "Still just a little bit of youth involved because he didn't hit his spots at times, but that happens."
Penn also missed his desired location on a curveball to Ivan Rodriguez immediately following the Palmeiro error. Fasano said the pitch was supposed to be off the plate, but hung over enough for the veteran to drill it into left field for a ground-rule double.
"The hardest thing for me, I knew going into it, was to stay back and keep the ball down," Penn said. "But I was rushing a little bit and kept some balls up."
Pitching coach Ray Miller said Penn will be even better when he is able to settle down and let his off-speed stuff work for him.
"You guys didn't really get to see his good changeup today," Miller said. "He was overthrowing it. He has a chance to be a good pitcher, whether he stays here or not."
Miller has seen a fair share of young hurlers in his 37 years in professional baseball. He said he tells each one the same thing just before they make their debut.
"My speech on the way in is about how I never got to pitch in the big leagues," he said. "I never got to make that walk. I tell them I am going to share and enjoy this like it's mine because I never got to do it. I think that kind of comforts a kid."
Penn said he was happy to get all of his firsts out of the way, including his first look at 35,955 screaming fans and his first home run allowed.
"If you get those things out of the way, now it's all fun," Penn said.
By fun, Penn means a meeting Thursday in Boston with the World Champion Red Sox, whose offense pounded the Yankees for 17 runs Saturday.
"I told him the next start will be easier because everybody will hate you," Miller said.