Cox was handed a western derby berth after Sean Darcy was cut down by concussion a week earlier.
Luke Jackson was Fremantle's main man in the ruck on the way to 29 hit-outs, 16 disposals and a goal, with Cox left in a secondary role.
The American-born Cox finished with 13 hit-outs, three clearances, four disposals, two marks and 0.1 from 59 per cent game time.
They were hardly stats to set the world on fire, but the 35-year-old came close on numerous occasions to taking important contested marks in attack.
If even a few of them stuck, Cox would have walked away satisfied with his work.
Darcy has a chance to return for Saturday night's clash with Carlton in Perth.
But even if he needs another week to recover, Fremantle coach Justin Longmuir has the option of playing Jackson as his sole ruckman.
"I thought he competed well," Longmuir said of Cox's derby performance after the 14.13 (97) to 5.11 (41) win, which improved Fremantle's record to 5-1.
"I think he'd be the first to admit that he probably left four to six or eight marks out there.
"He got his hands to a lot, but just didn't quite clunk them. But yeah, I thought it was a serviceable performance."
In an amusing side plot to Sunday's derby, West Coast used their banner to take a cheeky dig at Longmuir.
After he'd said during the pre-season that "there's no fun in my life", West Coast wrote on their banner: "Dockers Are Purple, Eagles Are Gold And Blue, We Have Fun In Our Lives, How About You?"
After helping Fremantle clinch their ninth win from the past 10 western derbies, Longmuir was asked if he liked the banter of the banner.
"Not really, but I don't get too caught up in that," he said.
Then after an awkward pause, Longmuir added: "I'm having fun now because we won. I hope they're having fun."
