Jordon Mutch's stoppage-time strike earned Cardiff a first away win since their top-flight return.
Mackay praised Chilean midfielder Medel for his impact on the game and Mutch for his match-winning strike.
The Scot is content with Cardiff's position early in the season.
"We've got a real belief after six games, about our ability to play at this level and be at home at this level," Mackay said.
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