The Dallas Mavericks expect to agree to a three-year, $33 million contract extension with center Dwight Powell in the opening stages of free agency Sunday evening, sources confirmed to ESPN.

Powell recently exercised his $10.3 million player option for next season with the plan to work out an extension to stay in Dallas long term.

The Mavs consider Powell, 27, a key member of the supporting cast for their pair of young stars, Rookie of the Year Luka Doncic and Kristaps Porzingis, who is expected to formally agree Sunday to the five-year, $158 million maximum contract that has been planned since Dallas traded for him midseason.

Powell, acquired by the Mavs as a throw-in in the otherwise ill-fated Rajon Rondo trade, fits well with Porzingis because he has the ability to defend power forwards but play the center role on offense. Powell has developed into an elite finisher on pick-and-rolls, averaging 1.33 points per possession in those situations last season according to NBA.com statistics, ranking second in the league among 31 players with at least 150 such possessions.

Powell, who averaged 10.6 points and 5.3 rebounds in 21.6 minutes last season, could become a full-time starter for the first time next season depending on how the Mavs address the center position in free agency.

Dallas, which enters free agency with $28.8 million in cap space, is prioritizing perimeter defenders who are good 3-point shooters as well as seeking quality depth at center.

The New York Times first reported the expected terms of Powell's extension.