His velocity wasn't a problem that day. Rosario's fastball sat at 94-96 mph, but he's since come to learn harder isn't always better.
The Dominican-born Rosario, who the Marlins signed as an international free agent on July 2, 2004, opened the season at Triple-A New Orleans, but he's already made two stints in Miami thanks in part to better use of his stuff.
"The difference from previous years is the changeup is helping me," Rosario said. "Before, I used to have a fastball and slider, and the day the slider wasn't working it was fastballs for everyone."
Also aiding Rosario was a tip Marlins pitching coach Randy St. Claire gave him: Vary the speed of your slider.
"I'm throwing it slower," Rosario said. "When I came up in 2010 I was throwing 96 (mph) and my slider was 90. Everybody was sitting hard. Now I throw it 84, 85. Sometimes I'll throw it harder."
Rosario at age 25 spent most of 2010 in the low Class A South Atlantic League and dominated. He paced all minor league relievers with 125 strikeouts and issued just 17 walks in 92 innings. Last season, he split time between Double-A Jacksonville and New Orleans and logged a less impressive strikeout-to-walk ratio (50-to-22) in 54 innings, contributing to why he made just four appearances for the Marlins.
He did get valuable closing experience, converting 23 of 29 opportunities for the Suns. The Marlins installed Rosario as the New Orleans closer this season and he excelled in the role again, saving 16 games and striking out 24 while walking two in 26 innings.
"That's what I like to do," Rosario said. "I enjoy that. That ninth inning is what fires me up . . . I always have the mindset of not caring what inning it is. When I come in to pitch, I don't care if the game is 10-1 or 20-1. I always go in like the game is 1-0 with the same intensity."
• In his 11th professional season, New Orleans outfielder Chase Lambin recorded his 1,000th career hit. A Mets 34th-round selection in 2002 out of Louisiana-Lafayette, he has yet to reach the majors.
• The Marlins on May 31 placed top prospect Christian Yelich on the high Class A Jupiter disabled list with a concussion. He returned after nealry three weeks on the shelf.