PHOENIX (TICKER) — Less than three weeks after guiding the Phoenix Mercury to its first WNBA title, coach Paul Westhead left the organization Thursday to become an assistant coach for the Seattle SuperSonics.

Westhead joins P.J. Carlesimo’s staff after spending the last two years with the Mercury, where he compiled an overall record of 41-27.

“I’m happy to join the Sonics staff,” Westhead said. “P.J. and I have worked together and known each other for many years and I’m thankful for the opportunity.”

Known throughout his coaching career for his teams’ up-tempo style, Westhead’s 2006 Mercury squad shattered the WNBA record for scoring by averaging 87.1 points per game, nearly 10 points higher than the previous mark held by the 2000 Houston Comets.

Westhead followed that up by guiding the Mercury to its first championship by winning a decisive fifth game, 108-92, against the Detroit Shock on September 16.

“We are unendingly grateful for the commitment and leadership Paul provided from the day he joined the Mercury organization and for the role he played in bringing our franchise and city their first professional basketball championship,” Mercury general manager Ann Meyers Drysdale said.

A veteran of the coaching ranks, the 68-year-old Westhead has enjoyed success at both the collegiate and pro level, where he guided the Los Angeles Lakers to the 1980 NBA title. He also coached Chicago and Denver, compiling a 184-224 mark in parts of six seasons with the NBA.

Westhead was 285-233 in 18 seasons as a college coach at LaSalle, George Mason and Loyola Marymount, with whom he made three straight NCAA Tournament appearances and reached the “Elite Eight” in 1990.

“We are extremely fortunate to have Paul Westhead join our coaching staff,” Carlesimo said. “He will be a great resource to our talented players, and also to his fellow coaches.”