Manager Eric Wedge brought Wilhelmsen in with two outs and the tying run on second in the eighth inning, and he surrendered an RBI single up the middle by Jemile Weeks that ultimately sent the game into extra innings.
The run was charged to Oliver Perez, who gave up the double, with the blown save being Wilhelmsen's first in eight opportunities since he replaced Brandon League in the closers role last month.
Wilhelmsen then got out of that inning and worked a scoreless ninth as well, extending his own shutout streak to 21 consecutive innings. That ranks fifth on the Mariners all-time list for relievers behind Shigetoshi Hasegawa (28 2/3 in 2003), Edwin Nunez (24 in 1985), Charlie Furbush (22 2/3 earlier this season) and J.J. Putz (22 in 2007).
Going into Saturday's games, Wilhelmsen was tied with the Rangers' Robbie Ross for the second-longest active scoreless streak in the American League, trailing only the Angels' Ernesto Frieri (26 1/3).
Wilhelmsen is tied for second among AL relievers for strikeouts (52) and innings pitched (44 1/3).