Most of the damage was done in the first half, with the Power conceding eight of the opening 10 goals of the game and trailing by 53 points at the main break.
Primus challenged his team to lift in the second half, and was pleased by the manner in which his inexperienced players responded.
First-round draft pick Ben Jacobs (22 possessions) amassed 13 possessions and a goal after being moved from the backline to the midfield in the second half.
Jasper Pittard took the game on and finished with 17 disposals and a goal, while Andrew Moore, Cam O'Shea and Simon Phillips also showed plenty of promise.
The youthful nature of the team has been used as an excuse for the club's poor start to the season, but Primus said it wasn't the young players letting the team down.
"I think all our young players today stood up, showed a bit and showed where they're going," Primus said after the game.
"Where we're at [on the AFL ladder] at the moment is because players apart from them aren't in good enough form and aren't playing to the standard that's required at AFL level.
"They're putting too much of the load on our young guys, so we've got to keep talking to them [in regards to] what they need to do to make sure we're a consistently good club."
Fremantle was able to gain an advantage in the first half by out-running the Power, who have had their work rate repeatedly questioned this season.
Port Adelaide won the clearance (39-38) and contested-possession counts (126-125) on Saturday afternoon, but Freo ran harder to create and win the uncontested ball.
"It's been an issue all year with our uncontested stuff," Primus said.
"Fremantle came with that tactic [to out-run us] straight away and we were let down by everyone on the field in that first quarter-and-a-half in terms of being able to keep with them when they spread and their ability and want to work hard."
The start is Port Adelaide's worst to a season since 2000, and has put pressure on the club to play more experienced players like Chad Cornes, who is being kept out of the team, as part of the rebuilding process.
Primus vowed to continue showing faith in his young players, saying Fremantle was a perfect example of a team now benefiting from blooding youth in previous seasons.
"We have a firm belief of how we want to play and what players are going to go towards our future," he said.
"We're going to keep batting down the path and not be swayed by whatever it is that's trying to sway us. That doesn't mean we're just playing kids and have given up winning. We want to win and we wanted to win today.
"This is the way to go about making sure you become a better team, and a better team for year after year not just one year, which is what we're trying to strive to do."
