Seattle optioned Wilhelmsen to Triple-A Tacoma on Tuesday. He instantly took the mound in Tacoma, pitching two innings in a day game.
Wilhelmsen was solid early in the season but had struggled with his command of late. He had 18 walks in his last 23 1-3 innings after walking just eight in his first 24 innings this season. Wilhelmsen had converted 24 of 29 save opportunities this season.
Capps is on his second stint with the Mariners. He appeared in 33 games with a 2-2 record and 6.37 ERA earlier this season.
Seattle also announced it was recalling Franklin Gutierrez from his minor-league rehab assignment, although he remains on the disabled list, and released outfielder Jason Bay, who was designated for assignment late last month.