Collingwood's Mick Malthouse is the latest AFL coach to admit he's struggling to come to terms with the controversial substitution rule after the Magpies opened their premiership defence with a 75-point demolition of Port Adelaide on Saturday.

Malthouse toyed with the idea of keeping his substitute Brent Macaffer on the bench for the entire game before he eventually came on in the final term as the Magpies smashed the Power 24.11 (155) to 12.8 (80).

It was another example of how the controversial new sub system will pose new challenges for coaches as they manage their interchange rotations.

Port counterpart Matthew Primus did not have such a luxury - he had to activate sub Cameron Hitchcock after key forward Jay Schulz suffered a knee injury in the second term.

Schulz will be out of action for at least a month with medial ligament damage.

Malthouse said he had thought about keeping Macaffer on ice so they could put more fitness into other Collingwood players.

"All the other players looked like they'd jumped on the slow bus, he was down here at Albert Park (at the Grand Prix)," Malthouse said of Macaffer's time on the ground.

"These are the dilemmas that we will all be confronted with - how much game time does your sub get? More importantly, how much game time does he get over seven or eight weeks (before their first bye)?

"We'd like to think the players who are playing all have some sort of evenness in their game (time)."

St Kilda coach Ross Lyon said after Friday night's match against Geelong that deciding on when to activate the sub was "Russian roulette".

While Lyon had to make his decision in the midst of a tight game, Macaffer entered with Collingwood in complete control.

Trailing by 45 points at halftime, the Power hit back with six goals to one and were only 16 points down in the third term.

But the Magpies kicked the last four goals of the quarter and the game was over.

"It's so evident - you clear the ball, you put massive pressure on the backline, you will generally score," Malthouse said.

"The time when they got back in the game, we just did not adjust in the stoppages, we got cleaned up."

As the premiers clicked back into gear, Port showed good signs before they were swamped.

"The biggest thing was the disparity (in) their size and their ability to keep playing at a fair intensity, compared to ours," Primus said.

"We were able to match them at times, but then our ability physically and mentally to stay in the game dropped away."

Midfielder Dane Swan and half-back Ben Johnson were best for Collingwood and Chris Dawes kicked four goals.

Matt Thomas was solid in the midfield for Port in his 50th game and kicked three goals, while Justin Westhoff also kicked four.

Leon Davis was a late withdrawal from Collingwood's team because of illness and Macaffer took his spot.

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