BOSTON – The Celtics lost their first preseason game.

So what?

The preseason is not about wins and losses. It's about learning. It's about growing as a team. It's about laying the foundation that, in this case, the Celtics hope will lead them to another NBA title.

It's a process that they went through during the 2007-08 season, when the new Big Three was formed. All that team did was go on and win the 17th world championship in team history.

And with all of the new faces on the team this year, it's a process that they are going through once again.

The Celtics learned a lot about themselves in their 96-90 loss to Houston on Wednesday night, but they still have a lot more learning to do.

Perhaps the most important thing they learned is that superstar forward Kevin Garnett, who was playing in his first NBA game since March 25, looked pretty good in the 13 minutes that he played.

Garnett is not in the best shape, but he was able to get up and down the court "without any pain."

"I felt good," Garnett told reporters after the game. "I thought I ran well. Spring-wise, I was not where I want to be. I didn't play for a whole quarter and, after six months, you've got to warm it back up, you know what I mean? For the most part, I felt great out there. I wasn't hesitant out there. There was no pain. I'm still not where I want to be. Like I said, it's a process."

Garnett scored six points (all in the first quarter) and recorded five rebounds and two steals, leaving the game for good 5:16 into the third quarter.

"I thought he played great in the first half," Rivers said after the game. "I thought he got stiff in the second half."

"I saw his gait and I thought four minutes into the second half he was exhausted," Rivers added. "I was just watching his gait as far as his legs and as long as he wasn't limping, I was going to let him try and bust through the wall. But then I thought, let's get him out."

Garnett said that he wanted to stay in the game in the second half but, "that's not up to me. It's not going to be something that's going to change overnight. Like anything else, it's a continuation. It's a process. Obviously, playing against the guys we have on this team every day, you have no choice but to get better. I just wanted to see where I was.

"For the most part, the talking, reaction, it was all there for me. Everything's coming back. Doc's on my rear end about attacking and being aggressive, and all that's just flow. The game is so fast and I was just trying to take it all in and let it all come back to me. It's all flow. It's all repetition and getting back into the flow. [I was] like a kid in a candy store, running around with his head cut off. I just have to slow down a little bit."

The big question remaining is: Will Garnett be healthy enough to go full-speed once the regular season starts? He still has a long way to go. The Celtics learned that Rasheed Wallace will fit into the Celtics system, and that he is still a good defender and 3-point shooter who will stretch the floor for the team.

Wallace was 1 for 3 on 3-point attempts, scored six points and blocked three shots, though he was faked out by Brian Cook, giving up a layup to him. The Celtics also learned that Wallace will not tone down his shouting at the refs antics. He was given a technical for doing just that.

They learned that Marquis Daniels is as athletic as advertised. He finished with seven points and five assists, looking like a pure point guard at times while backing up Rajon Rondo (7 points, 3 assists), but he also has the ability to play the two guard, and small forward positions.

"Marquis Daniels … I thought he may have been the best player on the floor today," Rivers said. "I thought he was terrific."

What will his final role be?

Michael Sweetney led the Celtics with 10 points and rookie guard Lester Hudson had 9 points and 3 rebounds.

"It was a good first game," Rivers said. "There were a lot of things that I was really happy with. This is about what you want out of an exhibition game."

The Celtics will get another chance to learn more about themselves Friday night when they host the New York Knicks at 7:30 at the TD Banknorth Garden.

If Garnett's legs aren't too sore, Boston's starting five will get another chance to grow as a unit. This will be the third season that Garnett, Rondo, Ray Allen (8 points), Pierce (8 points) and Kendrick Perkins (3 points, 3 rebounds) will start for the Celtics, and Rondo and Perkins have improved by leaps and bounds since this tandem was brought together two years ago and the Celtics won the NBA title.

If Boston's Big Three can remain healthy, they will have arguably the best starting five in the NBA. As for right now, they are just learning a lot more about each other.

roblee@projo.com