Chalmers stepped up while LeBron sat down, scoring 25 points and helping the Heat hold off the pesky Oklahoma City Thunder, 104-98.
Now the Heat have control of the series, leading 3-1 with Game 5 coming Thursday at American Airlines Arena.
Chalmers, whose 25 points were a career playoff high, said the Heat were determined to avoid another Game 4 finals loss and the ghosts of last year.
"Last year," said Chalmers, in an interview that appeared on CBS' New York affiliate. "We still got that taste in our mouth. We're all hungry and we don't want to have that feeling again."
The Heat were down by as much as 17 points in the second quarter, but edged back to within three points at the half before engaging in a seesaw battle throughout the second half.
Russell Westbrook scored 13 straight points for the Thunder, keeping the game close midway through the fourth quarter.
Westbrook, who has been criticized for shooting too much in the series, kept the Thunder alive with his playoff-best 37 points.
But the story of Game 4 was Super Mario, whose clutch layup with LeBron on the sidelines gave the Heat some breathing room, enough for Miami to hold off the Thunder.
Chalmers said when one of the Big Three goes down that's the cue for someone else to step up, and on this night Chalmers made his move right on cue.
"I just come out here and do what I have to do for my team to win," he said.
That is exactly what the 2012 version of the Heat are doing to a man, and all indications are LeBron's championship drought is about to end.