"Yeah, it did [surprise me]," Mattheus said. "It caught me off-guard. You try not to predict when the call's coming, because it's just counterproductive for your performance."
Mattheus said he was initially frustrated at spending time in Syracuse after missing most of Spring Training with chest inflammation. Though the results don't indicate he was a lock-down pitcher there, he said the time in the Minors was necessary.
"Spring Training was tough, so it probably was the best thing for me to go [to Syracuse]. At the time, I didn't really embrace it, but I needed the workload. Everybody else broke camp with 12, 13, 14 appearances. I needed to build back up."
Mattheus allowed six runs in 10 innings of work with Syracuse, but said the numbers don't reflect how his arm and stuff feel on the mound.
"The velocity was good, the arm felt great, but the results were mixed," he said. "Wasn't happy with the numbers, and they were a little misleading. The work I put in was more important than the actual numbers."
Mattheus' callup story was certainly an unusual one. He didn't even finish his Sunday outing, getting ejected after one pitch -- that didn't even hit the batter -- before receiving the summons to join the Nationals in Houston a few hours later.
"The night before, we had a few guys thrown at, and we were issued warnings and we didn't retaliate or anything," he said. "I pitched the eighth inning against this unbelievable talent, Gregory Polanco. … You can get him out with a sinker, but have to throw in on him.
"I threw one inside, and he was diving in. He didn't go down or anything, and it was almost over the plate. Then I got tossed. That was just wild. I went from that, feeling kind of incredulous, to being back up here."