Wilhelmsen, 28, has 19 saves and a 1.51 ERA in 32 appearances since replacing Brandon League. His only previous blown save came July 6, when he entered in the eighth with a 1-0 lead and allowed a run in a game the Mariners wound up losing in 11 innings.
The two runs in Friday's loss were the most he's allowed since becoming closer and the three hits were the first time he's given up more than two in a single-inning appearance. But the thing Wilhelmsen was kicking himself for was walking Dewayne Wise on four pitches after Gordon Beckham singled to short to start the inning.
What happened in that wild ninth inning after Seattle had rallied with six runs to take the lead in the top of the frame?
"They hit the pitches that I threw," Wilhelmsen said simply. "But you can't walk the go-ahead runner and I did that."
After Kevin Youkilis singled to tie the game, Paul Konerko ended it with a single that slipped out of right fielder Eric Thames' glove after he and center fielder Michael Saunders collided as both went for the line drive in the gap.
"That ball was driven pretty well," said Wilhelmsen. "It didn't look to me like either one had a shot, so I was really impressed with their effort. It was enough to get the guy in."
Manager Eric Wedge chalked it up as a tough learning experience for the first-year closer, including the knowledge that he couldn't afford the walk to Wise that ended up being the winning run.
"He understands the gig," Wedge said. "That's where you really put your back up against the wall in that situation. But you know what? You hate for him and for us to have the game end the way it did, but he'll be better for it. When that inning started, he wasn't even thinking about being in the game. The emotional range was from one extreme to the other. He'll be better for it. That's the first time he's had to do that."