Leesman took a perfect game into the seventh inning and struck out a career-high nine, but the Kannapolis Intimidators fell to the Lakewood BlueClaws, 3-2.
Warm weather, the left-hander said, was the key to his strong outing.
"Definitely, I'm not a big fan of cold weather, so it helped me tonight," Leesman said of temperatures in the mid-70s at Fieldcrest Cannon Stadium. "When it's cold out, it takes me a lot longer to loosen up and get warm. Sitting in the dugout on a cool night takes a lot out of me."
Leesman cruised through six innings before surrendering a two-out single up the middle to Phillies' 2007 first-round pick Travis D'Arnaud. The 22-year-old southpaw struck out Jim Murphy to end the frame.
"I was aware. I was just thinking after the fifth, 'Hey, it's a perfect game,'" Leesman said. "And then I realized, 'That's five, that's six.' I didn't take it onto the field, but really the only time I thought about it was then I went 3-0 on a batter. The last thing I wanted to do was walk someone."
The Cincinnati native, who did not walk anyone on Friday, recorded the first two outs in the eighth but was pulled after Sebastian Valle reached on a throwing error by third baseman Jon Gilmore. He lost his shot at a win when reliever Tyson Corley allowed an RBI single to Troy Hanzawa.
The 2008 11th-round pick said the BlueClaws were doing their best to mess with his rhythm and concentration on the mound.
"They kept trying to call time, three times, guys were rubbing their hands in the dirt, doing it over and over, so it was a little frustrating," he said. "I got [D'Arnaud] 0-2, but I threw a pretty hittable ball."
Leesman was charged with an unearned run on one hit over 7 2/3 innings, lowering his ERA to 2.95.
Last June, he became the second-highest draft pick in Xavier University history. He signed late and made his Minor League debut last Aug. 21 with Rookie-level Bristol before getting promoted to Kannapolis eight days later.
Friday was the longest outing of Leesman's brief career and the longest by an Intimidators pitcher this season. Despite the eventual outcome, he was content with the effort.
"Between Spring Training and the day I got here, I've tried to find the balance point," he said. "Once I found it, the confidence came back and I really started throwing. Tonight was definitely a confidence boost."
Leesman, whose fastball lives between 92-93 mph, said he sprinkled in a changeup and a curve to keep the BlueClaws off-balance.
"I really wanted to go at least eight innings," he said.
Leesman, who fanned seven on April 22 against Greenville, struck out three consecutive batters between the first and second innings and whiffed two more in the third. He got one more in the eighth.
Originally drafted by the Twins in 2005, Leesman said he'd like to earn his way up to Class A Advanced Winston-Salem sometime this season, if all goes well.
"I'd like to keep my ERA below three," he added. "It's tough, I know, but after this game it should definitely drop. I just want to make the best of my first full year, see what I'm capable of.
"I got up to 94 [mph] once this season, but just that day, it was warmer," he said. "I came back down after that, so it just needs to be warm enough."
Danny Wild is an editor for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.