The Dockers (18-2) locked in a top-two berth and set a new club record for wins in a season with their 37-point victory over the Western Bulldogs on Friday night in Perth.
Scores were level at half-time as the Dockers struggled to break through the Bulldogs' flooding tactics.
But the power of Josh Treacy in attack eventually broke the dam wall, with Fremantle kicking seven goals to one in the second half to secure the 11.12 (78) to 5.11 (41) win.
Treacy finished with 3.2 to go with eight marks, with his huge grab early in the final quarter sparking a game-changing four-goal burst.
Longmuir was proud with how his players problem solved their way through the flood of numbers.
"There were probably times in the first half where we were a bit spooked by their numbers back," Longmuir said.
"I thought as the game went on, we started shifting the ball a bit more and trying to shift their numbers, and that worked.
"Largely we knew that was the sort of game we were going to get, and we were prepared for it, and I thought the players worked through it pretty well."
Fremantle's ability to score heavily in short bursts has become their biggest weapon this season, but the Bulldogs' flooding tactics were able to contain the ladder leaders for two-and-a-half quarters.
So is Longmuir worried other rivals will try the same tactic?
"Good luck," he said.
"It tends to happen at times, and we've probably faced teams rolling around from the open side really heavily against our tall forwards this year.
"There's probably just a few more numbers back tonight. But we have faced it.
"They've probably got a couple of issues down back with their size as well with (Rory) Lobb having to play up the ground.
"So I think it's probably more circumstantial for them. I don't think we'll face that sort of look in the finals."
The Bulldogs entered the match without forwards Aaron Naughton and Cody Weightman, but coach Luke Beveridge denied his team had actively gone in with flooding tactics.
Fremantle won the inside 50m count 54-38, with the Bulldogs largely limited to attacking on the counter.
"It wasn't by design that we had saturation and numbers behind the ball," Beveridge said.
"We wanted to press up at different times, and we didn't get our execution right.
"We came here to win the game, not to be safe, not eliminate risk. But we didn't execute well enough.
"At the time in the game when we were in there from the scoreboard perspective, we had momentum opportunities, we fumbled the ball, or we mucked up gilt-edge chances, and we fuelled Fremantle's game.
"You're not going to win too many games with 41 points and below 40 entries and we didn't plan to play that way. It's just the way it turned out."
5°C