Now Knicks fans have another reason to hate Kevin Garnett.

Forget the January flare-up with Carmelo Anthony. Overlook the 52 rebounds he grabbed for the Celtics in the last three games of the Eastern Conference first-round series. Garnett has done something that already has impacted the series in a damaging way for the Knicks.

He taught Terrence Williams professionalism.

“I’ve got to be professional,” said Williams, one of the Game 5 heroes for the Celtics, who now seek to even the series 3-3 Friday night. “It’s one thing I learned from Kevin. I look up to Kevin so much, more now being on a team with him. Playing against him, you hate him, but now I look up to him like a big brother. So watching him work every day I kind of molded it into my game, so I’ve just got to be ready.”

Williams was ready when it mattered for the Celtics in Game 5. Having gotten virtually nothing at point guard from defense-first Avery Bradley, the Celtics sought anybody to combat Knicks pressure and quell Boston’s turnover epidemic.

So coach Doc Rivers weighed every pro and con and ultimately went with a real sabermetric style approach.