Milwaukee Brewers Wilhelmsen graduated from
Tucson High School, whence he was selected by the
Milwaukee Brewers in the seventh round (199th overall) of the
2002 Major League Baseball draft. Later that summer, upon signing with the Brewers on August 19, he received a US$250,000
bonus. He began his professional career the next season. Wilhelmsen played for the
Arizona League Brewers and
Beloit Snappers in 2003, going a combined 5–6 with a 2.84 ERA in 17
starts. Following that season, he twice tested positive for
marijuana and was suspended for the 2004 campaign. He decided to quit professional baseball during extended
spring training after his suspension ended in 2005.
Seattle Mariners Prior to the 2010 season, Wilhelmsen attempted a comeback and signed a minor league contract with the Mariners. He won his first major league game on August 15, pitching a perfect 8th inning against the
Toronto Blue Jays. On June 8, 2012, Wilhelmsen recorded the save in a six-pitcher combined
no-hitter which was started by
Kevin Millwood who left the game after the 6th inning due to a groin injury. The six pitchers used by the Mariners tied the record of most pitchers used in a no-hitter with the 2003
Houston Astros. The Mariners beat the
Los Angeles Dodgers 1–0. Wilhelmsen said after the game that while he was pitching, he had forgotten it was a no-hitter, and only remembered after catcher
Jesús Montero reminded him. Wilhelmsen was optioned to Tacoma on August 6, 2013, and recalled in September. In 2014 Wilhelmsen was back in the Mariner bullpen, appearing in 57 games and finishing the season with a 2.27 ERA and a WHIP of 1.05. It was also in 2014 that Wilhelmsen reached a wider audience in baseball after his formidable dancing ability was captured on video. During the 2015 season, Wilhelmsen had a brief stint on the
disabled list after a bullpen accident; Wilhelmsen was swinging his arms when teammate
Danny Farquhar ran into Wilhelmsen's right arm, resulting in a hyperextended elbow. On January 13, 2016, the Rangers and Wilhelmsen agreed to a one-year, $3.1 million contract to avoid arbitration. Wilhelmsen had a rough start with the Rangers with an ERA of 10.55. With this, the Rangers optioned Wilhelmsen to the Triple-A
Round Rock Express, but he refused, making him a free agent.
Seattle Mariners (second stint) On June 22, 2016, Wilhelmsen signed a one-year contract with the Seattle Mariners. He was designated for assignment by the Mariners on November 18, and released on November 22.
Arizona Diamondbacks On February 10, 2017, Wilhelmsen signed a minor league contract with the
Arizona Diamondbacks. He made the Diamondbacks'
Opening Day roster. He was designated for assignment on June 11. He was released on June 16, 2017, after struggling with his command, allowing 12 walks in 26 innings and posting a 4.44 ERA for the Diamondbacks.
Milwaukee Brewers On June 22, 2017, Wilhelmsen signed a minor league contract with the
Milwaukee Brewers. He was released on August 5.
San Diego Padres On February 5, 2018, Wilhelmsen signed a minor league contract with the
San Diego Padres. He was released on March 19.
St. Paul Saints On May 2, 2018, Wilhelmsen signed with the
St. Paul Saints of the independent
American Association of Independent Professional Baseball. He made 18 appearances for the Saints, compiling an 0-1 record and 2.89 ERA with 14 strikeouts and seven saves over innings of relief.
Toros de Tijuana On July 3, 2018, Wilhelmsen signed with the
Toros de Tijuana of the
Mexican League. He made 15 appearances (13 games finished) for the Toros, he compiled an 0-1 record and 3.86 ERA with 11 strikeouts and eight saves across 14 innings of relief. Wilhelmsen was released by Tijuana on August 18. Wilhelmsen announced his retirement on December 10, 2018. ==Pitch mechanics==