That leaves a group of eight others vying for three spots. Among the eight, only Diekman has heard this unorthodox question from his pitching coach: "You have an agent?"
That's how much Rich Dubee liked Diekman's arm and chances to make big-league money after watching him throw just a few times in spring training a year ago.
"After the initial, 'OK, thanks for the compliment,' I knew I'd have to make do on it and prove him right," Diekman said. "I feel like I did that about 50 percent of the time last year. It was an up-and-down season."
Up: He struck out three of the four batters he faced in his major-league debut in mid-May to earn a victory against Houston.
Down: Two days later at Wrigley Field - the ballpark he visited often as a kid - he nervously took the mound against the Cubs in the ninth with a five-run lead and coughed up four runs while recording just two outs in an excruciating 8-7 Phillies loss.
Up: He finished the season with a 1.50 ERA in his last nine appearances after returning from triple-A Lehigh Valley.
Down: He walked 20 batters in 271/3 innings.
Diekman, 26, had more ups than downs in his spring-training debut Sunday against the Detroit Tigers. He threw first-pitch strikes to every batter he faced and struck out Torii Hunter and 2012 American League MVP Miguel Cabrera with nasty sliders before giving up an RBI single that leftfielder Zach Collier misplayed in the wind. The one negative was a leadoff walk to Austin Jackson after being ahead in the count, 0-2, to the Tigers' leadoff hitter.
"I need to put away the hitter and move on," Diekman said. "I felt good about the day, but that walk kills you. Leadoff walks will kill you."
In an attempt to become more consistent, Diekman spent the offseason doing towel drills, a routine in which a pitcher snaps a towel in an attempt to repeat the release point on his delivery. He doesn't mind the practice; his father, Paul, had an obsession with preparation.
"When I wanted to start learning [golf], my dad wouldn't let me on the course for, like, three years," Diekman said. "He said, 'Go to the range every day, because when you go on the course I don't want you to embarrass yourself.' I hit so many balls before I hit the course. It was brutal. But I got pretty good."
Diekman's dream in his senior year of high school was to become a golf pro. He had played on the golf team at Southern, a tiny high school in Wymore, Neb., with a graduating class of "about 29." The Raiders did not have a baseball team.
"I had an application to the Golf Academy of America," Diekman said. "I was going to go to San Diego. I had it all filled out."
He never sent it because he also fell in love with baseball even though he played only 21/2 months of the year with an American Legion team. In a state tournament game, he struck out 17 batters, allowed one hit - and lost.
"The other guy threw a no-hitter," he said. "I don't want to talk about that game."
Colleges became interested. So did professional teams after his sophomore season at a junior college in Kansas. The Phillies drafted him in the 30th round in 2007, and he signed despite having a scholarship to Nebraska. In 2009, he went from a struggling starter with an overhand delivery to a reliever who threw sidearm.
"Nobody wants to face him," Phillies special assistant Dallas Green said after watching Diekman's inning Sunday. "He just has to throw strikes."
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