CLEVELAND — One preseason game playing alongside Mo Williams already taught the Cavaliers one lesson:

Be ready to run.

“They know they have to get out and run, because I’m gone,” Williams said.

Cavaliers All-Star LeBron James is quickly learning that.

“He’s very fast and quick getting the ball up the court, so it’s definitely a different feeling,” James said after the team’s preseason opener Tuesday night against Toronto.

The Cavaliers are back in action tonight against the defending champion Celtics for a 7:30 game in Providence. Boston ended Cleveland’s season a year ago in a grueling seven-game series in the Eastern Conference semifinals.

Fastbreak points were at an absolute premium for the Cavaliers in that series and for much of the season. And while coach Mike Brown promises the Cavaliers will never resemble the Kings of a few seasons ago or the Suns of recent seasons, they do want to get up and down the floor quicker this season.

The less they go against set defenses, the less James has to work against double- and triple-teams in halfcourt settings. With the speed of Williams, in addition to the quickness of returning guards Daniel Gibson and Delonte West, the Cavaliers look far more equipped to push the ball.

On Tuesday, the results were good early and spotty thereafter. Nine fastbreak points in the first 10 minutes were the good. But some shaky decision-making and playmaking later on was the bad.

“We did some things we’ll continue to get better at,” Gibson said.

The Cavaliers expect much more of the good to come for two simple reasons — the continuity that will develop through more time spent together and by getting physically used to running more.

“We’ve got to continue to get better, and we’ve got to get in a little bit more shape,” James said, “because our offense is geared on us running first and then breaking down and getting into our sets.”

As fast as Williams played at times Tuesday, that’s nothing compared to what he wants to do consistently.

“I just need to get back in basketball shape myself,” he said. “We have just got to push through the tired times right now. That’s what training camp is all about. We want to be an up-tempo team and push it at times, and we have to get our legs ready for it. ... Once I get my legs under me where I can play heavy minutes, I’ll be fine.”