The Boston Celtics lost to the Los Angeles Lakers on Christmas, to the Golden State Warriors a night later, and to Portland on Tuesday despite the Trail Blazers missing their best player, injured Brandon Roy. That made it official.

The Celtics are tired. They're the defending champions getting everyone's best game and laboring to keep up with the demand, and that's in addition to being the Celtics, a demand unto itself. People come at them no matter what.

It is a strange concept two months into the season for a veteran roster and a practiced coach, all of whom know about pacing and how there's nothing real to win in December. It's also in underlined contrast to the recent franchise-record 19-game winning streak and the 28-5 record even after the three losses in four games that, heavens, set them all the way back to a 70-win pace.

Except that the Celtics themselves admit they are feeling it.

"I was warned a lot about that before the year from coaches who had won it," coach Doc Rivers said. "When I asked, 'Well, what do you do?' they all said, 'There's nothing you can do about it. There's no way around it. You still have to win the games. As hard as you think they're coming, they're coming even harder than that.' We have found that to be very true.

"Like I've said all year, at some point it has to be a good thing for us to get attacked every night and to go through it and to win games and win games on the road – tough, hard-fought games. There's got to be some good in that. I don't know where it's at right now, but the way I look at it, there has to be something good about that."

Is there a better chance it helps the Celtics in the long run or hurts? "I don't know," Rivers said. "We're going to keep our minutes the same. But just because you are down on your minutes doesn't mean you are down on your mental fatigue. I don't know the answer to that question, and I won't know the answer to that question."

Or at least he won't until it may be too late.

The other problem: The minutes aren't down, and the depth isn't nearly as good as in the 17th championship season.

The Celtics were built on a foundation of veterans, played until June 17, went about an extra quarter-season in the playoffs, had five more postseason games than any other team, got older, lost important reserves … and have kept pounding the minutes in 2008-09.

Kevin Garnett is 32 and played 97 games last season from late October to mid-June. He averaged 32.8 minutes in the 2007-08 regular season. In 2008-09: 32.9.

Paul Pierce is 31 and played 106 games last season. He averaged 35.9 minutes in that regular season. In 2008-09: 36.6.

Ray Allen is 33 and played 99 games in the title run. He averaged 35.9 minutes in the regular season. In 2008-09: 35.8.

"No, I have not been surprised at how well teams have played against us, but it is hard scouting teams," Garnett said after the welcome easy win Sunday at Arco Arena, after the losses to the Lakers and Warriors and before the loss to the Trail Blazers.

"I am a person who watches a lot of film. I am a person who takes a lot of pride in knowing personnel. And I've watched a team the last three games and then actually played against that team and they look nothing like the three games in which they've played prior to us playing them."

Opponents get up for the Celtics unlike anyone else, in other words.

So it is that the intrigue has become not merely Boston vs. the field – the Cavaliers and Lakers foremost through the first 40 percent of the title defense, maybe the Magic, Hornets and Spurs – but Boston vs. itself. The Big Three are averaging more time or essentially the same amount as in the 2007-08 regular season while an unproven mix needing the work to mesh.

It's worth noting that each had a big jump in the playoffs – Garnett to 38 minutes a game, Pierce to 38.1, Allen to 38. They know exactly how much energy will be needed in the tank come the third weekend of April and the start of the playoffs. And the improvement by point guard Rajon Rondo, from the greatest of the unknowns in his first season as full-time starter to likely All-Star consideration in 2008-09, spreads the workload beyond the Big Three.

But the Celtics also had James Posey getting nearly 25 minutes a game off the bench and P.J. Brown clocking about 18 the final two rounds of the playoffs after signing in February and Sam Cassell as a backup point guard. This time around, Posey is in New Orleans after getting a better free-agent offer, Brown has gone back into retirement until further notice, and Cassell is on the roster in name only. He has yet to play.

Boston is shopping to upgrade the bench, especially up front. Brown is a possibility as a second-half addition again. Robert Horry – after previously saying he would consider playing only for the Spurs, Rockets or Mavericks because they are likely playoff teams close to his Houston home or Orlando because he could take his kids to Disney World – has not ruled out the Celtics.

That's the level of concern about the depth and the minutes and the toll of life as the defending champion. Or maybe the Celtics will mount another long winning streak and pull so far ahead of the pack that Garnett, Pierce and Allen will be using chaise lounges on the bench by March and they can finally get some peace and quiet before the playoffs, the time when they'll get attacked with something at stake.

Call The Bee's Scott Howard-Cooper, (916) 321-1210.