“Passing the torch” is a tradition as old as sports.

Right now, the Celtics are trying everything in their power to hold onto it — but they’re dangerously close to losing their grip.

When Kevin Garnett and Ray Allen teamed up with Paul Pierce, it was understood there would be a relatively short window of opportunity.

It’s been propped open for perhaps the last two seasons. But how much longer can it hold?

Down 3-1 and facing elimination tonight in Miami, the C’s “Big 3” is faced with its biggest challenge since coming together four years ago.

Another Big 3. A younger Big 3. Maybe even a better Big 3.

“These are those moments, when you write papers, books, poems, quotes. Whatever it is, these are those moments,” Allen said.

If Boston lives up to it, the C’s and the Heat could be back in the Hub Friday.

If they don’t, you can find that torch in South Beach.

Tale of the tape

Game 5 Wednesday
7 p.m., TNT, WEEI

» The situation
Miami leads Boston 3-1 in the best-of-seven Eastern Conference semifinals. This is do or die for the C’s; if they lose, the season’s over.
» The line
Miami -7, with a 181 over/under (both sides at -110).
» What’s next
Game 6, if necessary, is Friday (time TBA, ESPN). Game 7, if necessary, is next Monday (8 p.m., TNT).
»The keys
Frankly, it’s hard to see Boston pulling this one out. They had a wonderful chance to even the series at home in Game 4, but blew it with an awful possession at the end of regulation. When you’re getting beat by Chris Bosh, you know things aren’t going well. Miami just needs to keep the ball in the hands of Dwyane Wade and LeBron James. They’re stars for a reason.