After the Magpies gave up a 31-point lead in the first quarter by failing to kick a goal to the Bombers' five, they wrestled back momentum and levelled the scores by half time.
They then wrung out a 23-point victory despite being forced to reshuffle their backline with Alex Fasolo (toe/illness) and Clinton Young (corked thigh) unable to finish the game.
Vote for your top three players from Collingwood's stirring ANZAC Day win in the Magpie Army Player of the Year Award.
The way the game was won – different to the Pies' other three victories this season – was the most satisfying aspect for Buckley and enhanced his belief the team has improved this season.
"We are not putting a cap on what we are capable of, this side," Buckley said afterwards.
"We are still finding our best balance, we are still finding out what we are capable of and we look forward to challenges we have to come.
"Last year if we were to give up that many inside-50s we would have been scored (against) really heavily.
"We were a top four side defensively and offensively through the middle of last year in transition, contested ball and clearances, but at either end we had some work to do.
"We made some modifications, we are adjusting that.
"It was an excellent win. The pride in the performance, the belief in what we're doing at the moment...it's a massive step forward for us."
Anzac medallist Dane Swan summed up the Pies' first quarter as being "out-pressured" and "out-worked", which led to them chasing their tails and ensuring they didn't panic.
Buckley said the fact they worked out how to win and stuck to a new plan that evolved as the game changed was a major positive.
"I thought as much as you possibly can, our players held their heads and in the coaches box we held ours and understood it was going to be a grind to work out of it," he said.
"(Essendon) really had everything on their terms in the first quarter and we were able to wrestle that back.
"That was done on the run in many ways but it was done in the belief there are prerequisites with the way we want to play that we weren't able to execute in the first but we were in the last three."
They lost Fasolo in the second quarter and Young in the third, but it was the bizarre circumstances surrounding the former's fitness that left Buckley disappointed with the club's medical staff.
Buckley said they believed Fasolo had hurt his toe – and not his navicular bone again, as speculated during the game – before the main break.
He has also suffered from the flu for the past three weeks.
However, he ran out with the team for the start of the third and it took 10 minutes before the substitute was made to bring Josh Thomas into the game.
"I still have some questions to ask of our medical department," Buckley said.
"We had 20 minutes to work it out (at halftime) and it wasn't until 10 minutes into the third where we got the decision."
When asked if someone "might be having a kick in the bum", Buckley responded with, "Potentially, yeah".
Both players will have scans over the weekend.
Meanwhile, the Pies aren't expecting key position player Ben Reid to return before their round eight bye but are "bullish about him getting back pretty soon after".
Paul Seedsman will play his first VFL game on Saturday following pre-season hip surgery.
