Terrence Williams, who swears one year in China ironed the immaturity out of his game and attitude, is set to finalize a deal with the Celtics that will not only pay him through the rest of this season, but will guarantee him for next season as well, provided he makes the team. The deal will include several triggers that guarantee the contract in stages.

“Time will tell,” Celtics president of basketball operations Danny Ainge said yesterday of whether the talented swingman sticks.

Over a short period Ainge has been able to identify one special trait in Williams’ game. With Rajon Rondo out for the season, Williams is already the best passer on the roster.

“He’s a better passer than anyone on our team,” Ainge said. “He can play (point guard, shooting guard and small forward) and handle the ball. The reason I like Terrence is that we don’t have a true point guard. All of our guys can play the point guard in pinches, and all of them can share ballhandling responsibilities. But Terrence can be the best on our team right now.”