On March 27, 2002, he was traded by the White Sox to the Pittsburgh Pirates for Dámaso Marte. He spent the next two seasons pitching in AAA for the Nashville Sounds.
He was selected off waivers by the Minnesota Twins after the 2003 season. Guerrier made his Major League debut on June 17, 2004 against the Montreal Expos as the starting pitcher. He worked four innings and allowed two earned runs. On the season he appeared in nine games, making two starts for an 0–1 record and 5.68 ERA. He did not pick up his first win until September 23, 2006 against the Baltimore Orioles but he became a mainstay of the Twins bullpen. In 2008, the Twins lost primary setup pitcherPat Neshek to injury early in the season and Guerrier took over part of that role for a short time. He pitched poorly in the second half, however, sporting an 8.88 ERA. In innings, he was 6–9 with a 5.19 ERA. He improved greatly in 2009, posting a 5–1 record with a 2.36 ERA and leading the American League with 33 holds.
Los Angeles Dodgers
Guerrier agreed to a three-year deal with the Los Angeles Dodgers on December 16, 2010. He appeared in a team high 70 games for the Dodgers, the fifth straight season he pitched in at least 70 games. He finished the season 4–3 with a 4.07 ERA in 66.1 innings worked and became the first pitcher in baseball history with exactly one save in six straight seasons. In 2012, Guerrier pitched in 7 games in April and was then shut down with right elbow inflammation. He was placed on the 60-day disabled list and did not rejoin the Dodgers until the last week of August, ending his string of 5 straight seasons with at least 70 games pitched. Due to the injury, he only appeared in 16 games for the Dodgers in 2012, with a 3.86 ERA. He pitched in 34 games in 2013 with a 4.80 ERA before he was designated for assignment on June 30.
Chicago Cubs
On July 2, 2013 he was traded to the Chicago Cubs in exchange for Carlos Mármol. He appeared in 15 games for the Cubs and was 2–1 with a 2.13 ERA in 12.2 innings. He was shut down for the season in August after tearing the flexor muscle in his right forearm.
Second stint with Minnesota Twins
On January 29, 2014 he signed a minor league contract to rejoin the Minnesota Twins. The Twins released Guerrier March 24, 2014 a week prior to the end of Spring Training. He was re-signed the next day. He was designated for assignment on July 23. He elected free agency on July 29.
Pitching repertoire
Guerrier's most commonly thrown pitch is alternately called cutter thrown in the high 80s. He also has a four-seam and two-seam fastball, a curveball, and an occasional changeup to left-handed hitters.
