And Longmuir defended his decision to rest key players at the tail-end of the home-and-away season, insisting it was the right call to make.
Fremantle entered the finals series boasting a perfect 12-0 record at Optus Stadium this season.
But in front of 59,446 fans - Fremantle's largest ever home crowd - the Dockers barely fired a shot as Hawthorn kicked six goals to one in the first half on the way to a dominant 10.12 (72) to 5.10 (40) win.
It means Fremantle will have to beat either Carlton or Geelong in a home semi-final next week and then win an away preliminary final if they are to make the grand final.
The Dockers were the best team during the home-and-away season, with a 14-match winning streak lifting the club to a 19-4 record and the club's second ever minor premiership.
The shock loss to Hawthorn means Fremantle are now facing the prospect of a straight sets finals exit, but Longmuir is confident his players will bounce back.
"The facts are to get to a grand final we need to win two more games, two games in a row," Longmuir said.
"We've won 14 games in a row this year, so we've proven that we can win two games in a row.
"We've won on the road. We've won back-to-back road travels.
"It's not the way we wanted it to go, but we're not dead and buried. We've earned the right for a double chance.
"I've got full faith that we can get back to our best footy really quickly, and that starts next week."
Fremantle had secured a top-two berth with a month to go in the regular season, affording them the chance to rest some players who were managing niggles.
Sam Switkowski, Heath Chapman and Jye Amiss were rested for the final-round loss to Carlton, while Murphy Reid missed the last two games due to a testicular injury.
Josh Treacy, Luke Jackson and Caleb Serong were among the players to have their game time heavily managed against the Blues, while Alex Pearce missed the loss to Melbourne at the MCG.
Longmuir defended his tactics, declaring the decision to rest players were the right calls.
"Look at the guys we managed. Jye rolled his ankle at main training. He would have gone into that (Carlton) game not 100 per cent," Longmuir said."Murphy Reid had his injury. Chappy had a little bit of a hammy. We got that scanned. It came back clear, so he didn't really have an injury. But there's no point taking a risk on him."So if I had had those decisions to make again, and in hindsight, I'd make all the same decisions."
Defender Brandon Walker, who was brought in to tackle Nick Watson, will undergo scans after suffering a game-ending ankle injury late in the third quarter.
Former Demon Judd McVee could replace Walker for next week's semi-final, but key back Brennan Cox is no guarantee to return from a calf injury.
