And after one summer league game — a glorified scrimmage, really — the Heat are already noticing Cook's commitment on that end of the floor.

Cook scored 13 points in 23 minutes yesterday in Miami's 88-74 loss to the Charlotte Bobcats on the opening day of summer league play in Orlando. He earned high marks for his work guarding last season's No. 3 overall pick Adam Morrison, who went 2-for-6 from the field and had Cook guarding him most of the time.

"I felt comfortable out there," Cook said. "I missed a couple shots but I got in rhythm the second half. I competed. That's what I came out there to do. I felt like I played great defense ... felt like I had an all-around great game."

Cook — a standout 3-point shooter during his one season at Ohio State — went 3-for-4 from behind the arc, but misfired on all five of his shots inside it. But Heat assistant coach Erik Spoelstra, who's again serving as head coach for the summer league squad, told Cook before the game that his main focus should be on guarding Morrison, and said afterward that the 21st overall pick in last month's draft responded nicely.

"I thought it was a great challenge for him against a guy who started a little bit last year, the third pick in Adam Morrison," Spoelstra said. "That's what you want to look at from a defensive standpoint, someone who wants to take the challenge of guarding and taking away his airspace. And it was a challenge because he's a little bit bigger and they run a ton of screens for him."

Jermareo Davidson had 16 points for Charlotte, while Ryan Hollins had 15 and Morrison and Raymond Felton finished with 14 each for the Bobcats. Jeremy Richardson had 17 points for Miami, while Chris Quinn — the only member of the Heat's NBA roster in Orlando for the summer play — added 12.

Cook said there was some nervousness before his first NBA game, even though it was merely a summer league matchup held before an audience of league coaches, executives and scouts. He even suffered his first pro injury, banging his left hand on something early in the game and sporting a large ice pack afterward.

"I really don't know how it happened," Cook said. "I tried to bend it and it just started hurting. Ice it down and it'll be already. It's fine, nothing major."

The Heat asked Cook to spend the summer session of practices and games thinking about nothing but basketball — "practice, rest, practice, dinner, rest, sleep, come back the next day," is how Miami coach and president Pat Riley put it when asked about how he wanted the young guard to handle the next few days.

So far, Cook is taking that advice to heart.