It would require “something major” in the next 72 hours to stop Mayor Bloomberg from winning a third term Tuesday, a leading pollster said yesterday as a new survey showed Hizzoner with a double-digit edge.

A Marist College poll showed Bloomberg with a comfortable 53-38 percent lead over Democrat Bill Thompson among likely voters. Poll director Lee Miringoff said the chances of an upset are minimal.

“It would have to be a very, very unusual turnout and probably something major occurring this weekend,” Miringoff said.

Thompson pointed to polls released right before the 2005 mayoral election to show he can make a comeback.

“Look at the last election four years ago,” said Thompson. “They missed it by 20 points.”

Indeed, Bloomberg did less well in the ’05 election than polls predicted, but he still trounced his Democratic opponent that year, Fernando Ferrer, by 58 to 39 percent.

Both candidates pledged to keep campaigning to the very end.

“The field is littered with candidates who took the day off and thought they had it locked up. I’m not going to make that mistake,” the mayor said.