The hard-throwing right-hander acknowledged before Wednesday's game that reaching the 25-save mark was significant to him.
"Absolutely," he said. "They're all pretty meaningful."
But even as he's growing into the closer's role, the 28-year-old said he hasn't really changed anything in his approach.
"As far as the game goes, I don't think my mental level has changed much," he said. "Every single outing matters -- whether it's the seventh, eighth or ninth inning -- especially a year and a half into my career. So I just attack it all the same way. I haven't really had time to think about what it is to be a closer or whatever. I'm still trying to figure out what I do."
Wilhelmsen is a pretty relaxed individual away from the field, but he ratchets up his intensity on the mound. He said that adrenaline rush is something so unique that he's learned to harbor it even after games end.
"I really enjoy it, so I try to hang on to it as long as I can," he said. "On a good day, it only lasts five or 10 minutes out on the field. And, of course, there are the minutes leading up to it when you're warming up and you know the situation. But I don't know. It's definitely different than any other feeling I've ever had."
According to manager Eric Wedge, that drive is a big part of Wilhelmsen's successful makeup.
"He is very laid back and kind of just rolls with it," Wedge said. "But what you see when he's out there competing is a focused intensity that is real and allows him to thrive in that role."
Has Wedge ever had a closer who didn't have that intensity?
"Not very long, to be honest," Wedge said. "If you're going to sustain the closer's role, you've got to have the right heartbeat and temperament and attitude toward it. There's a degree of thick skin and toughness that has to go along with it."