Massachusetts Treasurer Tim Cahill announced Wednesday that he will challenge Massachusetts Democratic Gov. Deval Patrick in 2010 as an independent, creating a three-way race that appears likely to be a battle.

Cahill signaled his intention to enter the governor’s race when he recently switched his voter registration status from Democratic to “unenrolled” with a party.

Though his candidacy shakes up the race in ways that will have lasting consequences, he had to share the political spotlight in Massachusetts Wednesday with Christy Mihos, a Republican candidate for governor. Mihos’ campaign shot down speculation that he might switch to the upcoming U.S. Senate special election for the seat vacated by the Aug. 25 death of Democrat Edward M. Kennedy.

Cahill told supporters at his campaign launch in downtown Boston that as an independent, he would be free of party leadership that “encourages you to feel a certain way in a position or act a certain way or to say a certain thing.”