How do the Celtics lay such an egg?

PHILADELPHIA -- Where to begin?

The supposed showdown for the Atlantic Division lead turned into a walkover for the Philadelphia 76ers. They did everything they wanted. They got everything they needed. They even hit the century mark in points, delighting the 18,508 in attendance, who can get a free Big Mac.

Privately, they must have been wondering if the Maine Red Claws showed up instead of the Boston Celtics, who had won five straight, who had climbed to within a game of the division lead, and who were, in the words of their coach, Doc Rivers, in "the best place we've been in all year."

That was before the Sixers went out and crushed the Celtics 103-71. It was a wire-to-wire whuppin' with absolutely no silver linings or positives to be gained from Boston's perspective.

"This was one of them that you just throw away. You don't even go back to it, reference it, nothing. Just throw this one away," said Paul Pierce, who led what passed for the Boston offense with 16 points. "You can't explain it. We know this team isn't 30 points better than us. We know we're a better team than we showed."

The first meeting of the season between the two longtime rivals had some pregame buzz generated by the Celtics' streak, which had coincided with the Sixers dropping eight of 10. A Boston win could have vaulted the Celtics into first place for the first time this season.

Then, in their first two possessions, the following ensued: Ray Allen had his shot blocked by Jrue Holiday. Pierce missed a short jumper, got the rebound, then threw an outlet pass off the side of the backboard. It was quickly 6-0 and the Sixers never looked back, leading by double figures for the final 38-plus minutes.

"It doesn't matter who it is. I hate getting beat like this," said Allen, who had one of his worst games as a Celtic.

Among the lowlights on what could have been an interesting evening had both teams shown up to play:

• Allen going 0-for-5 from the field in 28 minutes of mostly pedestrian play. The last time he had gone an entire game without making a basket was nearly two years to the day, March 9, 2010, when he went 0-for-3 from the field while playing 34 minutes in a loss at Milwaukee. "I never got into the flow," he said by way of explanation. Then again, there was no flow to get into.

• The Celtics hoisted eight 3-pointers -- and missed all of them. The last time Boston went without a 3-pointer was Jan. 22, 2009 at Orlando, when the Celtics were 0-of-6 from international waters. You have to go back to Dec. 21, 2005 to find a poorer shooting night from 3-point land by the team. They went 0-of-10 in that game.

• The Celtics shot 35 percent from the field, which happened to be a season low. Their previous low had been 37.2 percent against the Hornets in New Orleans on Dec. 28, the third game of the season.

• It was easily the biggest loss of the season -- 32 points -- and the biggest margin of defeat in the new Big Three Era. This season, the low point had been a 19-point setback to the aforementioned Hornets on the aforementioned date of Dec. 28. Eight of the team's 18 defeats have been by more than 10 points.

Avery Bradley rattled in a pair of free throws with 26.5 seconds left to produce the final two points of the game for the Celtics. By doing so, the Celtics were able to avoid a new season low in points and instead match their current low, set Jan. 20 in a 79-71 loss to the Suns at TD Garden.

Marquis Daniels played.

• Allen, Pierce and Garnett were a combined 9-of-29 from the field for 26 points. Over their previous five game winning streak, the each member of the trio was averaging more than 17 points a game and shooting better than 50 percent from the field.

Evan Turner now has a personal highlight DVD for his kids and grandkids thanks to the generosity and largesse of the Celtics' defense. The second-year pro from Ohio State had a career-best 26 points and continually flustered any Celtic who got in his path.

Mickael Pietrus missed his only shot and then left the game in the third quarter, along with the rest of the Boston VIPs. He's 6-of-21 from the field in the past four games and 2-of-15 from 3-point territory.

• Rebounding. Do we have to go there again? Afraid so. The Celtics were outrebounded 57-38 on Tuesday night by the Rockets and somehow lived to tell about it. They were mauled again on the glass by the Sixers, who outrebounded them 54-35. That's two straight games with a minus-19 on the boards. Frankly, that is embarrassing.

• The Celtics have played 11 back-to-backs this season (and still have the back-to-back-to-back coming in April.) They are 5-6 in the second games, which breaks down thusly: 5-0 at TD Garden and 0-6 on the road.

Pierce is right about this one. You forget about it. Unfortunately for the Celtics, another young, frisky, athletic team awaits on Friday night in the Portland Trail Blazers. Then it's on to the Left Coast and the start of the much-dreaded eight-game road trip. That trip begins with two games in Los Angeles, and ends in, yup, Philadelphia on, yup, the second night of a back-to-back. Oh, what fun!

Longtime Celtics writer Peter May is a frequent contributor to ESPNBoston.com.