Free-agent forward Boris Diaw has reached agreement on a three-year, $22.5 million contract to return to the defending NBA champion San Antonio Spurs, league sources told Yahoo Sports.

Diaw, 32, transformed himself into an indispensable part of the Spurs' championship fiber and his return was considered a vital part of management's plan to compete for a sixth franchise title next season.

The third year of Diaw's deal is partially guaranteed, sources said. Diaw is guaranteed $18.5 million over the first two years of the deal, sources said.

Spurs general manager R.C. Buford and Diaw's agent Doug Neustadt completed the deal Sunday, sources said.