Kevin Garnett will take the Madison Square Garden floor this evening to participate in his 1,453rd NBA game. He insists that he hasn’t considered there may not be a 1,454th. If the Celtics do not defeat the New York Knicks tonight, their season will be over — a 4-1 Eastern Conference quarterfinals exit. One of the first questions that will follow is whether Garnett’s career, too, will be at an end. But the Big Ticket doesn’t want to consider the fact he may be punching his ticket to retirement. Such thoughts can only get in the way. So when he sat his 6-foot-11 frame down at the C’s practice facility yesterday, his vision was sharply tunneled. He seems to play most every game as if it could be his last. But would this one be any different because it could be, you know, the last? “Not really. Game 7’s an all-out,” said Garnett, echoing a team theme that every game now is a Game 7, even though tonight’s is, indeed, Game 5. “That’s just what they are, the last opportunity to survive. Your mentality can’t be anything different.” The last-dance card was played again, but KG wasn’t having any of it. You can bet all you have that a man like him has run the options through his head more than several times. Hell, he’s even acknowledged that he thought long and hard about retiring after last season before coming back and signing a three-year free agent contract. The deal guarantees him money, but it doesn’t guarantee he will stay around to collect on all of them. So if he did spend yesterday morning wondering what Thanksgiving on a beach would feel like, he wasn’t sharing that later. And he didn’t want to ante up for any hypothetical poker. “I’m thinking about the game Wednesday, and pretty much I haven’t thought about post-, after,” Garnett said. “I’m focusing on what it’s going to take to get to the next game.” Not even a serving of a healthy Rajon Rondo and what that would be like next year interested him. “I haven’t even given it any, like I said, even any type of next year, post-, pre-, nothing,” he said. “I’m just trying to focus on this game coming up. The challenges of being on the road are very difficult, obviously. We have belief that we can win on the road. Obviously it’s all about going out and doing it. They play very, very well at home, so our work’s cut out for us. We’ve got to be ready.”