Black said the O'Sullivan decision was an especially tough one to make. The Valhalla High (El Cajon, Calif.) graduate grew up a Padres fan and signed a Minor League contract in December.
He impressed during Spring Training and had his contract selected by San Diego on July 12. In seven appearances this season, three of them starts, O'Sullivan posted a 3.96 ERA.
"He pitched his butt off in Tucson -- probably the best overall starting pitcher there for a long time," Black said. "When we brought him here, he came up and did some nice work for us.
"He was on board, a native San Diegan who grew up a Padres fan, nice guy, good on the team, all those things. So it was tough. But we just felt at this point we made a baseball decision."
Boxberger was told he would be recalled Sunday and joined the club Monday. Boxberger has made just six relief appearances for San Diego this season -- most recently June 22 against Los Angeles. He has allowed four earned runs in nine innings.
Both Black and Boxberger mentioned the word "consistency" when asked what exactly they would be looking for in Boxberger's fourth stint with the big league club this season.
"Overall, I've worked on the command of my pitches and being able to throw any pitch in any count, being able to get ahead of hitters and being able to pitch every day," Boxberger said.
Spending time back and forth between Triple-A and the Majors initially took a toll on the 25-year-old Boxberger, who had progressed evenly to the Majors -- never being sent down to a lower level.
"Bouncing up and down and not staying in one spot is a little different," he said. "It took me a little while to get used to. But once I figured out the mental side, it's a good transition."
Black wants to see Boxberger's back-and-forth journey end, saying, "Hopefully this is the time he [comes up], and he never goes back."
So how can Boxberger accomplish that?
"He's just got to get his pitches in good areas, get ahead in the count and put guys away," Black said. "He's got the weapons; there's no doubt about it. I think each time he comes back he feels more secure as a Major League pitcher."