Mackay felt his side would have been worthy of a draw but had to accept that Leandro Bacuna's free-kick - effectively the match-winner despite Libor Kozak's subsequent second - was the difference.
"I'm disappointed for the players, up to the free-kick we looked good value for getting something from the game," he said.
"We had plenty of the ball and were beginning to cause Villa some real problems.
"But it was a top-class free-kick. At this level that happens. Players at this level, on any given day, can put the ball in the top corner or produce a free-kick like that."
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