SAN DIEGO -- When the Padres called up Robert Stock for his big league debut in June, they knew they were getting a hard-throwing right-handed pitcher.

SAN DIEGO -- When the Padres called up Robert Stock for his big league debut in June, they knew they were getting a hard-throwing right-handed pitcher.

What they didn't know is that they were also getting a durable one.

Stock spent the winter of last season undergoing a new throwing program that increased his fastball velocity more than three miles per hour. He now hits 100 mph routinely and has topped out at 101 this season. He's fit right into one of the best bullpens in the National League -- in his 20 appearances this year, he's struck out 29 hitters and holds the third-lowest ERA in the Padres bullpen at 2.22. He also notched his first Major League win Thursday in the Padres' 13-inning victory over the Rockies.

But the most impressive factor is Stock's long-range durability -- something pretty unexpected from a bullpen arm with such high velocity. It shined Thursday -- with Stock recording three shutout innings against a formidable Colorado lineup. He yielded just one hit and one walk in his second three-inning relief appearance.

"I didn't expect him -- from a workload perspective -- to handle the multiple innings as efficiently and proficiently as he has," Padres manager Andy Green said. "If you look back at his history, nobody was ever asking him to do that."

For Stock, who made his big league debut on June 24 after spending nine years in both the Minors and the independent Canada-America Association, his rising confidence in his command comes in direct correlation with his rising velocity on the mound. When he was sent down before the last week of Spring Training, he had no doubt that he would debut at some time.

"I wasn't too concerned about the dates or getting called up or not," Stock said. "I knew that if I competed like I knew that I could, and got people out like I knew that I should, that I'd make it to the Major Leagues at some point.

"I was definitely confident knowing that I had gained velocity, and in general just pitching skill," he added. "When you're facing down -- for instance last night -- Nolan Arenado , if you feel comfortable believing that your stuff can get a guy like that out, then you're going to feel pretty good stepping foot on the mound."

Stock faced Arenado in the 12th inning of Thursday's game, and blew a 100 mph fastball by him for a called strike. He then followed up with a 99 mph fastball. Although Arenado would reach base safely on William Myers ' throwing error -- it was still a testament to how far how he's come both physically and mentally.

"I found that my command has improved as my velocity has improved," Stock said. "Cleaner mechanics, more efficient throwing, and having a little more confidence that this pitch is faster and more difficult to hit, so you're not trying to nibble the corners as much."

The Padres' bullpen has been the team's biggest success story this season by far, and with rosters expanding Saturday, the team will most likely continue to experiment. But Stock knows his value and now the team knows his versatility.

"Typically, you don't ask guys throwing 100 miles per hour to throw three innings for you, but I guess we're just crazy enough to do that right now," Green said. "It's actually played out really, really well for him and for us."

Worth noting

• The Padres announced an official date for the annual Padres On Deck Game, where the organization's top prospects will once again face off against the top prospects of the Texas Rangers. The game will be held on Sept. 27, with first pitch slated for 6:10 p.m. PT. Admission will be free to the event. Current Padres who have participated in the event include Eric Lauer , Luis Urias and Jacob Nix . The team has not yet announced a list of participants for this year.

• Right-hander Bryan Mitchell will make his first start since being sidelined for nearly three months with elbow impingement Monday in Arizona. As the Padres try to get an early jump on solving the pieces of their rotation puzzle for next year, they'll have to work around a six-man rotation with an off-day nearly every week.

"We're still in discovery mode as far as what guys are going to be with us going forward and he's got an opportunity with the work he's put in over the last couple of months on rehab to get back to the point where he's a part of our future," Green said. "He's going to have to pitch his way there, nothing's going to be handed to him. ... We have six guys in our rotation and multiple off-days, and the understanding that any time we hand the ball to one guy, it limits another guy's opportunity."

• Right-hander Rowan Wick was recalled from Triple-A El Paso to take the place of Kirby Yates , who was placed on the bereavement list. Left-hander Clayton Richard (left knee) was moved to the 60-day DL in a corresponding move. Wick has a 1.99 ERA in 20 games with El Paso this season over 22 2/3 innings.

"We've been hearing about him for quite some time about how live the arm is," Green said. "It's been real fastball velo -- not that we haven't seen that with the last few guys we've called up. He's going to fit right in."

• Outfielder Franchy Cordero played catch for the first time since going on the disabled list on May 28 with a bone spur in his elbow, but don't expect him to make a return before the end of the season. The odds are much higher for him to play Winter Ball this year, though Green said he probably wouldn't play as much as he did last year.

Katie Woo is a reporter for MLB.com based in San Diego. Follow her on Twitter @katiejwoo.