The midfielder has not always been first choice under Mackay but has coped well with the step up to the Premier League and has become a mainstay of the side since the Welsh outfit's promotion to the top flight for the first time in 51 years.
He proved the difference against a resilient West Brom side on Saturday, heading home superbly from Craig Noone's cross in the 65th minute to seal a 1-0 victory.
That marked City's first win in six attempts in the Premier League, and Mackay felt that Whittingham's contribution meant that he deserved to be on the winning side.
"He scored a goal from that position earlier in the season against Hull City," Mackay told reporters. "I'm delighted for him because he's been getting in good areas and he's been one of my most consistent performers this year.
"He had a period out of the side near the end of last season but came back in the summer with a renewed belief in his own ability, worked really hard on his body and has shown his ability to survive in the Premier League as a midfielder."
The victory lifts Cardiff to 14th in the table, but it could have been a different outcome had it not been for David Marshall's heroics in keeping the scores level in the closing stages.
He produced a superb late save to keep out Shane Long's firm header, and Mackay hailed the consistency of his goalkeeper.
He added: "Shane Long is someone at any point who can sneak into an area, he's scored goals regularly.
"But David Marshall has been immense for me. He didn't have much to do but that was a top save. He was the best goalkeeper in the Championship last year.
"He's showing now he's a proven Premier League goalkeeper. He's really matured.
"We have great belief in him, he's a calming presence on the back four."