The Dockers' knack of losing close games in 2024 reared again on Sunday when Sydney kicked the final two goals of the match to snatch a thrilling win at Optus Stadium.
Fremantle made a series of key mistakes in the last five minutes, leaving the players shattered after the match.
Despite the loss, it was a vastly-improved showing from the 78-point defeat to Geelong a week earlier, but Clark said it was still a result that cut deep and left him feeling "pretty damaged".
"To be over them all day and to lose like that, it's pretty heartbreaking," Clark said.
"There were just little things that let us down.
"Defending the lead, we want to try and keep the ball skinny. You want to be able to defend behind it.
"Kicks into the middle of the ground that get turned over - you can't defend behind those and they scored twice from it, so we let ourselves down in that area."
"But as much as it is heartbreaking, it's very promising we were able to compete with them as long as we did."
Fremantle entered the season full of confidence they could snare a top-four berth and challenge for the flag.
Belief in the player group remains high despite the 0-2 start, but a win against arch rivals West Coast in Sunday's western derby is simply a must.
"Positive as hell," Clark replied when asked about the optimism within the group.
"I think there's enough proof in the pudding to say you don't have to win the first five games to play finals.
"There's a lot to work on, and it's a long season. So it's a game of momentum.
"It doesn't matter if you lose the first two - it doesn't mean you can't make finals.
"That one (loss to Sydney) stings, but we're a pretty positive group. We'll bounce on from that."
West Coast copped an 87-point hammering from Gold Coast in their season opener, but they almost toppled defending premiers Brisbane at the Gabba last week before running out of steam on the way to a 19-point loss.
Key Eagles duo Jake Waterman (calf) and Jack Graham (hip) are a chance to return for Sunday's derby, while Fremantle will be without Brandon Walker (dislocated shoulder).
"They're a much improved team," Clark said of the Eagles.
"They've added some really nice players to their list.
"Derbies are always massive. It doesn't matter where you are on the ladder or how many wins you've got, it's always a hot and contested game."
