As a chorus of boos rained down at Miller Park as he walked to the mound, the Marlins' skipper pulled Conley four outs shy of a no-hitter at 116 pitches.
"It was easy right there," Mattingly said. "I knew he couldn't finish. We weren't going to let him finish. That was really easy, actually. If he had an easy inning there, an eight- or nine-pitch inning, we probably would think about it. But when he gets to that point, you know he's not going to be able to finish the game.
"This kid has a chance to be really special, so there's no way, at this point in the season, that we're going to let him go to 130."
Entering the eighth at 100 pitches, Conley needed five pitches to strike out Ramon Flores before issuing a five-pitch walk to Colin Walsh.
Conley then got Hernan Perez to fly out to center fielder Marcell Ozuna on the fourth pitch of his at-bat.
"I knew coming into the eighth I was already at 100 [pitches]," Conley said. "I was really, really happy that he let me go out for the eighth. I felt good. I was starting to get fatigued a little bit. I started having to work a lot harder to get the ball to come out the same. I'm happy I went out there for the eighth."
The competitor in Conley left "a big part" of him wishing he could have finished the game. Conley's previous career high for pitches was 106, while the most he had thrown in four starts this season was 95.
"I know what they are doing," Conley said. "I appreciate that they don't want me to go out there and throw 150 pitches or whatever it is to try to get a no-hitter. A no-hitter once is great, and it would be an honor. It would be an incredible thing to do in the game of baseball. It is not easy, but I intend on pitching a lot, so I don't want and they don't want to jeopardize the season."
Conley retired the first nine batters he faced before Domingo Santana reached on an error by shortstop Miguel Rojas. Conley then walked Jonathan Villar and Ryan Braun to load the bases with nobody out.
To escape the inning unscathed, Conley struck out Jonathan Lucroy and got Chris Carter to ground into a double play.
The 21 pitches Conley threw in the fourth inning likely were what cost him a chance at completing the no-hitter.
"It was after I got through the fifth that I started to settle down and get more consistent with the secondary stuff," Conley said. "But at the end of the day, what it comes down to is I threw too many balls. I put too many guys on for free. We had an error. Today just wasn't the day for it to happen. I'm at peace with it."
Jose Urena kept the no-hitter alive by recording the last out of the eighth inning and striking out Braun to start the ninth. But Lucroy ended the no-hit bid by flaring a single over the head of second baseman Derek Dietrich.
"All I know is it was 68-mph exit velocity," Lucroy said. "I really drove it. I'll take it."
Would Dee Gordon, suspended Thursday night for violating Major League Baseball's drug policy, have caught it?
"I don't know," Mattingly said. "Probably. Dee's pretty exciting. He probably catches that ball."
While the rest of the Marlins didn't arrive at the team hotel until after 6 a.m. CT after playing in Los Angeles on Thursday night, Conley was already in Milwaukee.
Conley at first fought the decision to travel early, but he eventually gave in.
"It didn't sit well with me," Conley said. "I felt like that was a right that you earn and not a privilege you are given just because of the day you are starting. I was told by Mattingly that he felt it was what was best for the team. I really respect his baseball opinion and really respect his opinion as a man. I got the blessing of some of the older guys, if you will."
From completing a four-game sweep of Los Angeles, losing their All-Star second baseman to suspension and nearly throwing a combined no-hitter, it was quite the 24 hours for the Marlins.
"It's been a roller coaster," Mattingly said.
Andrew Gruman is a contributor to MLB.com and covered the Marlins on Friday.