The tall targets have returned from serious knee injuries over the past fortnight and shape as key figures in the huge clash with Carlton on Saturday night, having combined well in last round's 26-point win over Richmond.
They claimed four contested marks and four marks inside-50 between them, with McStay adding three goals and Cox helping Darcy Cameron dominate the ruck battle.
Their presence over the final month of the season is crucial to the Pies' finals chances, with premiership forward Brody Mihocek (pectoral) ruled out for the rest of the year.
A raft of injuries to key players have meant Nathan Kreuger, Reef McInnes, Billy Frampton and Jeremy Howe have also been used as tall options forward of the ball throughout Collingwood's difficult campaign.
"For a long time we had different talls rolling through there and different people playing ruck," Cox told AAP.
"It was a bit of a merry-go-round at times but it's nice to have two stable people there in the forward-line.
"If we're slowed in play we can look up and know who to kick it to.
"It's pretty obvious, so it makes us a bit more predictable when we need to be.
"That helps us set up our defence and offence a lot better."
A concussion, along with a knee injury, suffered against Fremantle landed Mason Cox in hospital. (Richard Wainwright/AAP PHOTOS)
Cox spent time in hospital after suffering a a grade-two medial collateral ligament injury in his right knee, as well as concussion from a head knock, during Collingwood's draw with Fremantle in round 11.
The 33-year-old American had two months on the sidelines but needed just one VFL game on return before answering Craig McRae's call back to the senior team against Richmond.
"It's good to be able to be back playing with the boys because rehab can be somewhat of a lonely place for a long time," Cox said.
"I kind of felt normal. It was nice to get out there and not feel like you're out of breath or anything like that.
"It was actually a good feeling, so credit to the high performance staff.
"They've been awesome for me to be able to get back to where I'm at and play in the back half of the year."
Cox was nursing a sore right hand after the win over Richmond but dismissed concerns over the injury ahead of the Carlton clash.
"Someone punched the back of it, so it's a bit bruised," he said.
"But other than that, we're good."
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