The Marlins recalled Hatcher and Rosario from Triple-A New Orleans, and they optioned outfielder Bryan Petersen and lefty reliever Dan Jennings to Triple-A.
The hastily pieced together roster moves came after the Marlins bullpen was tapped out in a 12-inning win over the Padres on Friday night at Petco Park.
Adding two relievers gives the Marlins 13 pitchers and 12 position players.
Manager Ozzie Guillen says the balance may stay that way for a while, especially since the bullpen has been overused.
"I like pitchers," Guillen said. "Give me some pitchers, it makes things easier. When one guy goes down, the bullpen can be hurt for a long time."
On Friday night, the bullpen had to pick this up after Josh Johnson exited after 2 2/3 innings.
If a pinch-hit option is needed, Carlos Zambrano is a switch-hitter and a quality hitter, for a pitcher.
Hatcher and Rosario were with New Orleans in Iowa at the time they were told to pack up and get to San Diego.
Hatcher posted a 1.20 ERA in 15 innings for the Zephyrs, while Rosario has a 2.13 ERA in 12 2/3 innings.
"They showed they can pitch," Guillen said. "We'll see how long we'll take with them. We might keep them. Because the way we're playing, we're going to need pitching."