The Reds pounced on Marlins rookie right-hander Daniel Barone for six first-inning runs -- four on Ryan Jorgensen's first career grand slam -- to create a cushion large enough for Shearn to comfortably go seven innings on the way to a 9-3 win in the finale of the three-game series and Cincinnati's seven-game homestand.
"Even if it's only one day, I can smile," said Shearn, who waited 12 years to reach the Major Leagues. "This is what I've worked for my whole career. It was everything I thought it would be. The balls had tighter seams than Minor League balls. That's why I throw big league balls in the offseason, so my curveball would work."
Brandon Phillips and Edwin Encarnacion also homered for the Reds, who scored all nine of their runs in the first three innings on their way to extending their win streak to a season-high six games. Cincinnati's sweep of Florida was the team's third of a three-game series this season, all since Pete Mackanin was named interim manager on July 1. The Reds also swept the Diamondbacks at Great American Ball Park and the Braves in Atlanta.
Shearn, who turns 30 on Tuesday, played 11 seasons in the Minor Leagues -- he did not play in 2003 after undergoing Tommy John elbow ligament replacement surgery -- before being called up from Triple-A Louisville to the Reds to make Sunday's start. Since Louisville's home season is nearly over and he didn't want to pay a full month's rent to spend just a few more days in his apartment, he was living in the groundskeeper's camper in center field at Louisville's Slugger Field when he got the call from Bats manager Rick Sweet on Saturday.
Shearn immediately drove to Cincinnati, arriving at about 12:30 a.m. ET Sunday and cadging a spot on pitcher Gary Majewski's couch.
"I think I got to bed about 3 [a.m.]," said Shearn, who left 10 tickets for family and friends and estimated that about another 30 showed up to watch his debut. "When I found out that Ryan was catching, it took the edge off a little bit. I would've slept in my car to come up and pitch in the big leagues."
Shearn became the oldest Reds player to make his Major League debut since Greg Tubbs, who played in center field on Aug. 1, 1993, against San Diego at 30 years and 335 days old. Shearn is the oldest pitcher to make his Major Leauge debut with Cincinnati since Pat Scantlebury started against St. Louis on April 19, 1956, at 38 years, 160 days old.
Shearn admitted there were times when he felt like giving up baseball -- especially when his wife, Kelli, gave birth to their daughter, Riley, 18 months ago.
"My family's been so supportive," said Shearn, who's spent all or parts of the last five seasons he's been active at Triple-A. "They said, 'You're so close. Don't give up.'"
Working with his usual Louisville batterymate, Shearn gave up three runs in the fourth inning on Dan Uggla's home run. He allowed four hits with two walks and two strikeouts.
"I've probably caught 95 percent of his starts the last two years," said Jorgensen, who wore a jersey with his name misspelled in Sunday's game. "Knowing how a pitcher throws is important."
"That was an interesting battery," Mackanin said. "You have to tip your cap to Shearn. He did what you're supposed to do -- changed speeds, spotted his fastball. It's not easy pitching with a big lead, because you don't want to blow it.
"That was a great audition. It probably warrants another start. He was cool as a cucumber out there. He didn't look like he had any fear. He didn't look unnerved. He was talking to somebody out there, but I don't know who it was."
"I yell at myself," Shearn said. "You've got to talk to somebody. It's lonely out there."
The Reds already were averaging 6.8 runs per game on their most recent homestand before scoring six in the first inning -- all with two outs. Adam Dunn singled to drive in the first run, and Encarnacion's run-scoring single preceded Jorgensen's third hit and second homer of the season.
Jorgensen understood that, even with the home run, he's likely to be heading for Louisville since David Ross is expected to be activated from the disabled list in time to play in Tuesday's doubleheader.
"That's just the game," Jorgensen said. "I'm glad to see Ross is healthy and he doesn't have any repercussions from his injury. That's the nature of the game. I'll take it."
Phillips followed Ken Griffey Jr.'s two-out double with his 25th homer of the season in the second inning, and Encarnacion led off the third with his 10th homer of the season.
Mark Schmetzer is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.