Cosart, who is the subject of a Major League Baseball investigation surrounding his alleged sports gambling activities, missed his last start because of a blister on his middle finger. He returned to pitch six scoreless innings against the Washington Nationals, allowing just one hit.
He also made his strongest comments denying any involvement with sports gambling since the investigation began.
"I told all these guys, I never have, never will bet on baseball," he said, according to the Miami Herald. "That's the only statement I can come out with right now. I'm letting MLB security [handle the rest]. They've investigated my Twitter. I had to speak to some people from their offices last week, but I'm in a good position on it, I'm confident. Like I said, it's kind of just in the commissioner's hands now and we'll see what he does with it."
Cosart said he is hopeful that MLB's investigation will be completed by Opening Day.
Cosart, 24, allegedly exchanged multiple direct messages with a gambling authority on his Twitter account at an undetermined time, and the interaction became public when it was shared on the social media site by a third party. Cosart deleted his official Twitter account after screen shots of the exchange began appearing on the Internet last week.
ESPN.com's Jerry Crasnick contributed to this report.