To make room for Mata on the 40-man roster, the Orioles moved Mike Gonzalez (left shoulder strain) from the 15-day DL to the 60-day.
Castillo (1-0, 12.79 ERA) will be joining the Orioles for the third time this season, and was most recently optioned back to Norfolk following Thursday's loss to the Rangers. Given that Castillo didn't pitch well his last time out -- allowing four earned runs on four hits over just 2/3 innings in Texas -- he said he was surprised to get the call.
"But they've seen what I can do [in the past]," Castillo said.
Castillo has appeared in 48 games with the Orioles over the last two seasons, going 1-0 with a 3.32 ERA, and he will provide manager Dave Trembley with another left-handed option to go with long man Mark Hendrickson and lefty specialist Will Ohman.
The 26-year-old Mata will be making his Major League debut. A closer with Triple-A Norfolk, the right-hander recorded eight saves and was 2-1 with a 1.86 ERA in 18 games.
"Mata will be really excited to be here," Trembley said. "I know what his history is and what he's done, but I'm not at this particular point in time able to say what role he'll be in. He's in the bullpen."
Castillo and Mata will join starter David Hernandez -- who was also moved to the 'pen prior to Tuesday's game -- in giving Trembley a wealth of options. Ravaged by injuries, the O's have an eight-man bullpen and are hoping to find strength in numbers.
"It's challenging," Trembley said when asked if this was the most uncomfortable bullpen makeup in his nearly three years at the helm.
"But you never know, somebody might step up and it could not only be interesting but it could provide an opportunity for somebody to really make a name for themselves. So. that's how I look at it."