Considering where he stood about seven months ago, fresh off of a rare surgery he wasn't sure he'd recover from in order to pitch again, he has more reason than that to be surprised.
As he drove home from Toledo with a friend following his most recent rehab outing with the Triple-A Mud Hens on Wednesday night, he was thinking about his rough second inning of work when it dawned on him where he is.
"I looked at him and I said, 'Hey, man, it's really, really crazy that I'm throwing triple digits again,'" Zumaya said. "The doctors did not know how my arm was going to heal. It was like a 50-50 chance."
When asked about his toughest time through this whole process, he points to the day when he actually had to make a final decision on whether to have the surgery that would repair the AC joint in his throwing shoulder. It was his only chance to play again, but it also a virtually unprecedented surgery for a pitcher.
There was no history of a comeback from this injury from a pitcher. And even after Zumaya had it, there wasn't always hope on his part, either.
"It'll change you a little bit," he said. "You have to realize that this game will humble you quick. Just to realize what I've done, it's changed me a lot, staying strong and believing. Because I did lose hope after my surgery, and I never thought I was going to be here again.
"I had thoughts of retiring and just giving it up, and I'm here again. I'm close. I'm knocking right on the door."
The change is noticeable. Zumaya was a little quieter as he talked with reporters Thursday morning. The smile is still on his face, but he talks with the voice of someone who has matured plenty over the past two years. Physically, he's also much slimmer, having lost about 30 pounds since Spring Training, thanks to his workout program.
From a pitching standpoint, he said, throwing 100 mph isn't as important to him anymore. He thinks he could succeed throwing 95 if he had to. It's the symbolic importance, the fact that he can throw now as hard as he did before and answer questions. It proves a point to others, but it has also proven a point to himself.
"Some days, it felt like I had just come right back out of the operating room," Zumaya said. "I'd be like, 'Oh my god ... Is my arm fine?' And other than the first game I threw and a couple other games, it was just getting better and better. 'Is this really happening? Is it going to happen too fast? Am I pushing it too fast?' Every day, it just felt fine."
After his first game, he couldn't even play catch. On Thursday, after throwing Wednesday night, he felt like he could go out and pitch again. He was able to go out and play catch.
Those are good moments for him. It was one of those, he said, that led to one of his more infamous moments. After having a very good session this spring in Lakeland, Fla., he said he decided to celebrate by having some friends over. He was startled to find pictures of that night show up on the Internet, which he didn't realize until the Tigers' front office contacted his agent about it.
The pictures suggested someone who was partying through his rehab. Zumaya said he was being an average 23-year-old.
"Those pictures look a lot crazier than it was," Zumaya said. "It looks like I'm holding myself up and hurting myself. I was not putting any stress on my arm, I can tell you guys that. I've had enough setbacks in my life already. I don't want to have any more.
"It was upsetting. But that teaches you that you have to really watch yourself everywhere. I was in my own house, and those pictures were taken and I get a phone call."
Zumaya's setbacks, he hopes, are behind him now. Now, he's not only on the brink of returning to the big leagues in virtually his old form, he could make his return in his hometown of San Diego next weekend.
"It feels good," he said. "It felt good just pitching in Toledo. Even when I did bad the second inning, they still applauded me. It felt really, really good that I have people supporting me still."