The 32-year-old's deflected second-half volley helped move the Bluebirds 10 points clear at the top of the npower Championship.
And his manager believes Smith's display throughout the match showed why they were so keen for the former Watford man to recover from his hamstring injury.
"You can see why I'm glad to get him back; he's a top-quality player and he's someone I've known very well as a footballer and I know what he can bring to this club," Mackay told the club's official website.
"It was a really bad hamstring tear that he took when he was just getting into his stride in the team and I thought through the whole game he was exceptional.
"We knew that we were pushing him to the limit to get him to the point we did and thankfully I didn't take him off five minutes before, but that's management."