Mile Jedinak grabbed the opener for the Eagles before Craig Noone equalised a minute before the interval and Gunnarsson pounced to take Cardiff five points clear at the top of the Championship.
"This year we have a very similar sized squad to last year but there is more strength in depth and players go in and out on performance," said Mackay.
"It is about making sure you take your chances and grab it and Aron came in today and did that. He scored but also did exceptionally well in the second half.
"They are a great group with a lack of ego there and that makes them work hard for each other whether on the pitch, the bench or the squad."
Bluebirds goalkeeper David Marshall made a string of fine saves at the Cardiff City Stadium, while Palace midfielder Wilfried Zaha curled his shot off the crossbar, with Mackay admitting it took them a while to get going.
"It took until the half an hour mark for us to really get into the game and get on the front foot. From then on in I thought we were excellent," added the Scotsman.
"They got the message at half-time when we had a chat. I asked them their thoughts on where they thought their level of performance could go and they got there.
"They know if they work hard and step on like we did in the second half then we have footballers who can open team up and it is about patience and doing the correct things and that is what they did."