Cosart retired the first 18 batters and Justin Friend recorded his Minor League-leading 14th save Sunday as the Threshers edged the Bradenton Marauders, 1-0, at McKechnie Field.
The Phillies' top pitching prospect was perfect before Robbie Grossman lined a single into center field leading off the seventh inning. Cosart (4-3) competed against Grossman in high school in Texas.
"I honestly didn't really pay much attention until I turned and looked at the scoreboard after they got that hit and realized it," Cosart said. "It's kind of funny that their leadoff hitter, Grossman, got the hit."
Cosart, who also walked a batter before escaping the seventh unscathed, threw 96 pitches. On a 105-pitch limit, he was told he'd head out for the eighth if the Threshers added insurance runs. They did not against Porfirio Lopez, who combined with Jhonathan Ramos on seven innings of shutout relief.
Clearwater scored its lone run on Darin Ruf's first-inning RBI single off starter Jeff Inman (1-2). Rehabbing second baseman Chase Utley went 0-for-4 and struck out twice for the Threshers.
"I'm definitely not going to complain, handing the ball over to Justin," said Cosart, who had never taken a perfect game bid so deep. "He's been there in the eighth and ninth [before] and makes you feel pretty good."
Friend induced five straight groundouts before making Grossman his 16th strikeout victim of the season to end the game. The 24-year-old right-hander, selected by the A's in the 13th round of the 2007 Draft, has allowed one run on six hits over 19 innings for a 0.47 ERA.
"He came over from Oakland," via the 2010 Rule 5 Draft, Cosart said, "and they are missing out. He shouldn't be here. He's got great stuff."
Friend also has been an advisor to teammates. Cosart said the Oklahoma State product fixed his curveball grip.
"That helped tremendously today," said Cosart, who turns 21 on May 25. "He's pitched a long time and he knows what he's doing. It helps to have older guys."
The new grip was one in a series of tweaks Cosart made this week after allowing five runs over 4 2/3 innings on Monday at Dunedin.
"I throw harder, so I tend to try to do too much," he said of his struggles. "I was rushing, as my pitching coach was telling me, kind of jumping out and overthrowing and my command got sporadic. I quieted down my delivery, nice and easy. And everything is coming out smooth.
"All three pitches were there today. I was able to move in and out, up and down against a pretty good hitting team, and I just kind of carried it through the entire game."
After eight starts in the Class A Advanced Florida State League, Cosart is tied for second in wins and ranks third in innings (46).
"I just want to build on it and take it into my next start," he said. "To throw shutout ball, to throw no-hit ball, a perfect game, you have to have a little luck along the way."
A buddy in the bullpen goes a long way, too.