A week ago, the Celtics said they weren’t going to get all hot and bothered about their playoff seeding, and they sounded rather wise and prudent. They’re saying similar stuff nowadays, but they speak no longer from a position of strength. Now they cannot worry about their seed, because they are essentially powerless to do anything about it. With Kevin Garnett on an extended break to deal with left ankle inflammation — and let’s not even get into those who are gone for the season — the Celtics on any given night are playing a high-priced pickup game. Guys are jumping into the rotation in “I got next” fashion. In last night’s 100-85 loss to the Knicks — themselves without Amare Stoudemire, Tyson Chandler and Marcus Camby — the C’s were less than even the sum of their parts. They can be forgiven a tad for being slightly discombobulated, but they cannot be pleased with their lack of fortitude. When your opponent pulls in 15 offensive rebounds and beats you, 29-6, in second-chance points, that’s not entirely a team thing. Part of that is you getting sand kicked in your face and turning the other cheek. And when you turn the ball over 20 times, it’s not entirely a familiarity fault. Part of that is you lacking proper focus. The C’s actually had 17 fast-break points, which is harder than you think when you consider the drag from their “Hello, my name is” badges flapping in the Garden breeze. The Celtics are now in the seventh-seed position with Milwaukee breathing down their neck and 12 games left. The most encouraging thing the Celts have going for them now? Philadelphia. Had the 76ers gotten a few games out of Andrew Bynum and put up an effort that didn’t have coach Doug Collins barking at them in others, the C’s might be in some measure of danger regarding their very place in the postseason. Now they’re simply playing out the string and hoping to find a few workable assets from the new guys as Garnett and Courtney Lee make their way back. “We were going to do that anyway,” said coach Doc Rivers, “but, yeah, listen, the decision we’re making with Kevin’s the right one. “But we still want to win games. And we’re not going to let one game say that we’re not going to win any more games. It’s just silly to me to even think that way. We have to get ready for (tonight in Cleveland) and then go from there.”