The Cubs right-hander did joke he was fretting over his loss to manager Dale Sveum in the team bunting tournament.
"That kind of stuff stays with you for years," Dempster said, tongue in cheek. "I've had a lot of sleepless nights lately. Hopefully, I'll get through it."
What should be settled soon is the Cubs' Opening Day starter. Dempster was given the assignment last year, but Sveum wasn't ready to commit on Monday.
"We've given it some thought, but we haven't decided anything yet," Sveum said. "We're just waiting and seeing how things pan out. We'll have that done within the next week."
The deciding factors will be more than performance. There's an upcoming series against the Brewers from April 9-12, which Dempster will be included in. The right-hander is 15-5 with a 2.75 ERA in his career against Milwaukee.
Dempster said he doesn't need to know if he's starting April 5 against the Nationals at Wrigley Field to motivate him.
"I literally take it day by day," he said. "I'll let all that play out as it plays out. [Opening Day] is always exciting, but it doesn't change what my approach on the season will be, whether it's the first day or fifth day."
Dempster finished last season 10-14 with a 4.80 ERA. It was the seventh time he'd reached 200 innings, which was a positive. There weren't many other pluses.
"Any time you have a sub-par year -- I can only speak for me personally -- you don't really like that a whole lot and you want to do better the next time around," he said. "The easiest way to do that is go out there and work hard and be as ready as you can be, and I've done that this winter and this spring, and I'm looking forward to getting through here healthy and getting started."
On Monday, Dempster made his Cactus League debut against the Athletics and gave up one run on two hits and struck out two over two innings. Shortly after the workout, he was in the stands, talking to friends. On Sunday, he was spotted in the outfield berm with some buddies. That supports Sveum's theme this spring: Work hard, but have fun.
"There's been a lot of good things," Dempster said. "Every morning we have meetings and we really harp on the positive things that happen the day before, and we preach playing aggressive and attacking and believing in ourselves, and I think it's a good thing. There's a bright future on the horizon but also a bright future right now. A lot of good players in here."
Last season, Dempster struggled in the first month and was 1-3 with a 9.58 ERA. What happened?
"I forgot about last April," Dempster said. "I put that behind me."
What happened from May to September?
"I made better pitches, I executed pitches better," Dempster said.
"He had an unbelievable Spring Training," Sveum said of Dempster, "where he had unbelievable command of his fastball, and that might have gotten him into a little bit of trouble, because he mentioned he wasn't using his secondary pitches as much because he was so caught up in having great fastball command in spring. He didn't work on his offspeed stuff in Spring Training.
"The bottom line is, he knew he was better than he showed last year, and I think he's on a mission to prove that he's the pitcher he was before that."
Dempster said he's been working on all of his pitches this spring and did say his offspeed pitches were ahead of last year.
"You can work on fastball command just playing catch," he said. "I've been using my sides on my other stuff and my offspeed pitches so they're crisp when the season starts."
This is Dempster's ninth season with the Cubs and 15th in the big leagues. His seniority also is a factor in picking the Opening Day starter.
"That all goes into it, no question about it," Sveum said. "Who had the better year, the matchups, the leadership, who's been here the longest, stuff like that, longevity of a career. You can go on and on about the reasons why."
A good start is great. A good finish would be better. This also is the last year of Dempster's contract with the Cubs. He's noticed everyone in camp working hard to make a good impression on the new Cubs front office but says that's only natural.
"All those pieces fall into place if you just go out there and do your job," Dempster said. "The easiest thing for me to do is focus on my job, and that's preparing in between starts and every fifth day to go out there and do the best job I can of being mentally and physically prepared to pitch. Whatever happens, happens."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter@CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.