The Power was just 10 points behind the reigning premiers at half-time, but simply couldn't go with Geelong in a third term that saw the visitors outscored 11 goals to one.
"The first minute of the third quarter to the last minute of the last quarter was really disappointing, and we need to learn from it," Cassisi said following the 95-point defeat.
"We've got a really young group - I think we had 11 guys who've played under 60 games out there today and they had 11 who have played over 150 - so there's a bit of a gap there, but our competitive stuff wasn't there in the second half.
"We can’t shy away from that, and come Monday we'll review it. It's going to be pretty ugly at times, but that's what we need to do to move forward.
"The young blokes are very enthusiastic and they're eager to learn. They're really disappointed with this, but we'll look at the ugly stuff come Monday and then move on.
"We can't walk around with our heads down because we've got St Kilda next week."
Cassisi was pleased with the way Port Adelaide's on-ball brigade attacked the contest in the first half, but felt for his teammates at either end of the ground once that competitiveness waned in the second half.
"Winning that contested ball really needs to be our focus to give our forwards a chance," he said.
"In the second half we didn't do that, and it makes it really hard for our backs as well.
"I think Geelong had like 20 inside 50s in that third quarter, and you just feel really sorry for the backs because they were under fire and we didn't help them too much in the midfield.
"But you do get a real appreciation for Geelong's work rate when you're out there. The more times we can expose our young guys to high-pressure footy like that, the quicker they're going to learn and the better they're going to get."
