O'Donnell had to mark Grealish when the Aston Villa ace came on as a sub and picked up a yellow card for one crunching tackle.
And he revealed that John McGinn had told him to wind up his team-mate by being NICE to him, rather than slagging him off.
He told Scotland HQ: “I think (for the booking) I was just starting to get a wee bit fed up.
“He had just come on and normally when the fresh wingers come on and you're a wee bit tired you're just thinking, 'I need to hit him here'.
“I was getting fed up with him trying to take the mickey out of me so I gave him a wee hit!
“John McGinn had been giving me some tips. He said if (Grealish) comes on I had to get nibbling in his ear.
“But don't be critical, be complimentary. So the full time he was on I was telling him how good looking he was and that I loved his calves!
“I was asking him how he get his hair like that. John said that if you tell him he was hopeless or to kick him really, really hard he gets up and gets back at you.
"So maybe that was the advantage against Jack Grealish the other night.
“I also noticed he doesn't shave his calves!
"Most boys shave their legs as it's good for the masseurs but Jack's got massive calves and he doesn't shave them.
“So I said to him they must be so big the fact that he doesn't shave them and they still get spoken about!"