He finished his summer in San Francisco with a September callup by the Giants. There he posted a 1.04 ERA in 11 games, not allowing a run until his final outing and fanning 11 in 8 2/3 innings.
Small wonder that he is MLB.com's Minor League Reliever of the Year for 2009.
Even had Runzler been healthy to start Spring Training, it's unlikely anyone could have imagined the season in store for him.
A 2007 ninth-round Draft pick out of Cal-Riverside, Runzler had posted a 3.44 ERA in 15 games in the Arizona League that summer before moving up to Class A Augusta to open the '08 season. There he struggled with a 5.47 ERA in 20 games, walking 19 in 24 2/3 innings before being sent to join the short-season Salem-Keizer club for the Northwest League season.
After pitching part of the season on what was later diagnosed as a stress fracture on his landing foot, Runzler made sure he would get into pitching shape as early as possible to make up for lost time.
Once deemed ready, he was assigned back to the GreenJackets work group, where he became the primary project of first-year pitching coach Steve Kline, himself a veteran left-handed relief ace making his professional coaching debut.
"He taught me mechanics, but most of what he taught me was mental, about attacking hitters," said Runzler, who posted an 0.68 ERA in 19 games with the GreenJackets before his promotion to Class A Advanced San Jose. "It all started coming together."
But when Kline, a 6-foot-1 225-pound southpaw who retired midway through the 2008 season, looked at the 6-foot-4 230-pound left-handed Runzler, he didn't see a young Steve Kline.
"I saw another freaking Billy Wagner," Kline said, comparing Runzler to one of the most effective southpaw closers in the last decade, Wagner's diminutive stature notwithstanding. "He had such a great arm. All he needed was some confidence and a little luck."
At first, Kline was surprised to get Runzler, thinking a guy with that stuff would likely have headed right to San Jose.
"He had such a great arm, what was the problem? So I watched him throw and felt he just needed a little luck go his way," Kline said. "He started pitching well, and the confidence and the swagger came and it kept carrying over. He's a quick learner and has a really deceptive delivery."
When Runzler moved up to San Jose in early June, he rejoined his 2008 Augusta manager Andy Skeels, who had been tracking his progress from afar.
"It was one of those player development things where you knew if he could just get it figured out a little, he could be devastating," Skeels said. "And after two or three outings here, we started realizing we might not have him here for very long."
Indeed, Runzler continued to dominate with an 0.84 ERA in 19 games at San Jose, an 0.96 ERA in seven games at Double-A Connecticut in his next move up and finally two scoreless games at Triple-A Fresno in the promotion after that.
Through it all, Runzler and Kline kept in touch on a regular basis via text messages and phone calls. Kline, meanwhile, continued to get feedback from scouts who would come through town after having seen Runzler elsewhere.
"They'd say, 'Hey, I saw your kid throw the other day,'" he said. "All these people kept praising him."
Finally, Runzler got the ultimate call, and certainly one he could never have imagined when he got to Arizona in January. While sitting in the bullpen in Las Vegas, his manager told him that he was going up to the big leagues the next day.
"I was shell-shocked," he said. "I had no idea that was coming."
Needless to say, he called Kline for advice and got plenty.
"When he called me to tell him he'd gotten called up, I just told him to make sure he latched onto all those guys in the bullpen," Kline said. "Listen, learn and keep his mouth shut. But I was so happy for him. And I got to see him pitch in the big leagues when they came through Arizona, which made my day."
Runzler made his Major League debut Sept. 4 in an eventual 3-2 win against Milwaukee. Facing left-handed hitting veteran Jody Gerut with a man on second and two outs in a game tied, 2-2, he struck Gerut out on three fastballs.
Often a player who has cruised through the Minors will hit a bump when he reaches the big leagues for the first time. In Runzler's case, he carried his success almost seamlessly through his debut, with the lone blemish coming Oct. 2, when he allowed a solo homer to Padres catcher Henry Blanco in his final outing of the year.
"The one thing Kline kept telling me was that the game doesn't change at every level, you don't have to throw any harder or make your pitches break more," Runzler said. "The hitters get better and while they still have holes, you just have to attack every hitter. Of course, I was nervous up there, but once I got on the mound it all just felt good."
Kline wasn't the only "proud papa" watching Runzler's success. Skeels and the rest of the Giants player development staff looked on with pride and pleasure as well, for many reasons.
"He's one of the all-time quality kids you'll ever meet," Skeels said. "And when you watch his stuff, with that kind of makeup and competitiveness, his success is one of the true successes for player development in any year."
But with all of the coaches and managers who contributed to Runzler's season, Skeels emphasizes that the credit all belongs to the pitcher himself.
"He worked so hard at taking what he was taught, and it takes a lot of faith and confidence to take that out into the game," Skeels said. "It says a lot about the player. It's one of the things we're looking for: aptitude."