"I'm way more confident," said Cook, who made 71 appearances for the A's in each of the last two seasons. "That's like a double-edge sword, because I felt confident the whole time. To say I'm more confident is strictly because I felt good, not because I was doubting myself.
"Everything felt great, really good. Pleasantly surprised isn't the right term to use, because I'm not surprised, but I would say instead of optimistic, I'm confident. I don't want to say I didn't expect it to feel that good, but I was happy it did."
Cook limited his pitches to fastballs, but he said he had already been working on his offspeed pitches in flat ground sessions. He will most likely throw another bullpen this weekend and, barring any setbacks, face hitters in live batting practice next week in advance of his Cactus League debut.
"You start to feel like, wow, I can speed the process up and get in a game shortly," he said, "as opposed to, you're so far away and you see other guys get out there and compete and you really start to miss the competition factor of it all.
"I competed with myself a little bit today. I didn't try to blow anything out or try to go 100 percent effort-wise. I just tried to make pitches as if I was facing a hitter."
Cook still has a chance to appear in at least five or six exhibition games, a total the A's believe is enough to deem him ready for Opening Day. Asked if it was important to have two of those appearances come on back-to-back days, the 26-year-old responded, "I don't think that's really an issue."
"Especially with the strength of our bullpen," Cook said. "I think that I can get through the first little bit without having to do that. We talk about it all the time. I think our bullpen is really good."
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.