Written off before Saturday's game at the SCG, where the hosts were without five players suspended by the club, the Swans scored a stunning 53-point win in one of their best performances in recent memory.
"I guess it's a little hard when what happened happened, and all those really good players that normally play for Sydney didn't play tonight, for players to think in the back of their minds that this might be a little bit of an easier game than what it turned out to be" Fagan said at his post-match press conference.
"I tried very hard this week to convince our players it was going to be a tough game, we're going to the SCG, its Sydney's home ground.
"But somewhere back in their deep recesses of their mind I just wonder whether they really thought it was going to be as hard as what it was. Sydney were magnificent tonight."
Dunkley, who was one of Brisbane's better players tallying 24 disposals, 10 contested possessions and eight tackles, was certain complacency and underestimating the Swans didn't seep into his team's consciousness.
"That's something that I don't reckon crossed anyone's mind to be honest," Dunkley told AAP shortly before Fagan spoke.
"Finals footy we've learnt over the journey, anyone can win, you've got to be on your game. They were on their game tonight and we weren't.
"It doesn't really matter what personnel you put out there, we go into a game preparing for their best and so do they."
Sydney performed better in all key metrics, notching more contested possessions, inside 50s clearances and tackles.
"They were just harder and tougher than us and they wanted it probably  more right from the start," Dunkley said.
"You can make up excuses for ourselves, but at the end of the day they were too good, so we've got to lick our wounds and go again next week."
While Brisbane have repeatedly bounced back from poor games in the past three seasons to reach grand finals, both Fagan and Dunkley stressed they had to make that happen rather than hoping history will repeat itself.
Fagan and Dunkley targeted centre bounce as an area the Lions had to improve in after Sydney scored 6.3 from that source.
Noah Answerth came off in the first quarter with an ankle issue, but returned to the field later, though Fagan said he looked a bit sore.
"I will be interested to see how he pulls up tomorrow, I don't know how bad he is," Fagan said.
"It was a good sign that he was able to play most of the game out, and we took him out in the end when we had no hope of winning the game, so fingers crossed for him."
