Both pitchers are 20 years old and have never made an appearance above Class A Dunedin, but now they become front and center in Toronto's attempts at building a formidable bullpen following last year's disappointing results.
"They've been great, both of them," Blue Jays manager John Gibbons said of the two rookies. "I didn't know either one of them. I did see Osuna down in the fall league, but everyone in the organization was really high on them, and I can see why.
"They're ahead of the game because they're strike throwers. A lot of times, power arms like that, as young kids, that can be an issue, but both of those guys have done a great job with that."
Toronto has yet to make any official announcements on its bullpen for Opening Day, but the dismissal of Delabar from camp does seem to clear things up. Left-hander Brett Cecil will be the closer with Aaron Loup and Castro likely filling the set-up roles.
Marco Estrada, Todd Redmond, Colt Hynes and Osuna are the apparent favorites for the final four spots. Veteran lefty Jeff Francis also technically remains in the mix, while it's still possible the Blue Jays would contemplate carrying right-hander Kyle Drabek on the roster as well.
Drabek is out of options on his contract and cannot be sent to the Minors without clearing waivers. He has been considered a long shot for several weeks, but then again the demotion of Delabar came as a major surprise, so the Blue Jays clearly aren't averse to being unpredictable.
"It's starting to take shape, but we're not ready to announce anything just yet," Gibbons said. "I'm sure that will come over the weekend or the beginning of next week. We said when we got down here, 'Things are going down to the wire.'"
is a reporter for MLB.com. Read his blog, North of the
Border, and follow him on Twitter @gregorMLB. This story was not subject to the approval of Major League Baseball or its clubs.