Butler was likely to be unavailable on Thursday after throwing 26 pitches in his relief appearance the day before. It was just the second time he had pitched since being the last reliever named to the Cardinals' staff out of Spring Training.
Adding Rondon and Fornataro can also help the Cardinals stay away from Seth Maness, who threw a combined 40 pitches in appearances on Tuesday and Wednesday against the Brewers.
Both Fornataro and Rondon were already on the team's 40-man roster and made strong spring impressions. Rondon was the only pitcher in camp to stay around until the end and not allow a run. He pitched 9 1/3 innings and worked around nine hits and five walks.
"That was one of the things I wanted to improve on was trying to throw more strikes," Rondon said, with catcher Tony Cruz serving as translator. "I did feel like I had been trying to pick the corners a little too much instead of using the corners and trusting my stuff."
In five appearances with Memphis, Rondon allowed six hits and three runs.
Fornataro was sent to Minor League camp midway through Spring Training, but he has had as strong of a start to the season as anyone in the Memphis bullpen. Prior to the callup, he made four scoreless appearances, allowing one hit and notching a save.
"It's just exactly what we told every one of those guys when we sent them down," Cardinals manager Mike Matheny said. "It's going to come down to who is throwing the best at that time. You want to be that guy, just stay sharp and continue to work on certain things. We gave them all things to work on and it was very obvious that Eric had worked on some of those staying inside the zone and using the sinker."
Rondon, who grew up in Richmond, Va., said his father was driving up to attend Thursday's game at Nationals Park. The first appearances by Rondon and Fornataro will be their respective Major League debuts.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.