Through 11 games entering Tuesday, he was 0-0 with a 6.75 ERA in 9 1/3 innings.
During an early season AFL game, Munson was struck on his landing (right) foot by a hard-hit ball. He was sore for a while. He and Rafters manager Matt Williams said his command was affected somewhat, but he still has been able to maintain his routine.
"Things have been going all right. For a while, they didn't go as well as I wanted them to. I went through some tough outings, but I have gotten better, and that's the important thing," Munson said.
"Just like when you have some success and can't get too complacent, you can't get too down when things don't go your way.
"I have kept my confidence. My fastball command is back, and that helps set up the offspeed pitches."
He is encouraged by his effort and the possibilities that lie ahead.
"I wanted to show [the D-backs] that they made the right decision by having me come out here again," Munson said. "I've been working pretty hard. And it's been good to have Matt Williams [also the D-backs' third-base coach] out here with all the time he has put into the game."
The 23-year-old Munson is one of three D-backs relievers on the Rafters roster, with right-handers Evan Marshall and Eric Smith. Williams said they are interchangeable when they enter the game.
"They're all competitive and can work the 7-8-9 [inning] area," Williams said.
Munson, the D-backs' fourth-round pick in the 2010 First-Year Player Draft, spent the entire '12 season with Double-A Mobile, helping the team win the Southern League title.
He appeared in 44 games, going 3-5 with a 6.28 ERA, three saves and 64 strikeouts in 53 innings.
"You have to be aggressive, be in an attack mode most of the time, not a defensive mode," Munson said. "You have to have a killer instinct. And you have to have a selective memory. You have to be able to forget things, because this game can break you."
Munson was in the D-backs' camp last spring as a non-roster invitee. He hopes history will repeat itself in the spring of 2013.
"I am best as a late-inning guy," he said. "A lot of guys fit into the seventh- or eighth-inning range, but I think I can close in the big leagues. It's the best spot in the bullpen.
"You want to be that guy, to keep the game close. You know your team is counting on you. Most of the time, you have to go in and get those three outs, lock down the ballgame. There seems to be a lot more adrenaline. There's just something about it that feels like nothing else."