Benarbia, who has not started a league match for almost two and a half months, restored City's lead with a spectacular diving header and then played an exquisite throughball for Marc-Vivien Foe to seal victory.
Keegan was full of praise for Benarbia saying he has recovered from his early season dip in form and now will definitely start Saturday's match at Fulham.
Keegan said: "Ali hit the crossbar, scored and made a goal, dominated the match for the 20 odd minutes he was on and won the man of the match award.
"He is an unbelievable player and has proved he can play in the Premiership."There was also praise for Benarbia from Villa manager Graham Taylor.
He said: "He's a very talented player and the skill he showed setting up the third goal only a few can do.
"People will be saying why is he not in the side but maybe that is his best role, though Kevin must decide that."City showed no side-effects from the home defeat by Tottenham three days earlier and took a deserved lead in the 15th minute through Foe.
And only a brilliant save from Villa goalkeeper Peter Enckleman denied City a second goal as he thwarted Shaun Goater.
Villa, without an away win in the Premiership, came back into the match and there was no surprise when Dion Dublin equalised four minutes before the break.
Though the second half was lacklustre for long periods City had three great chances to go back in front as Foe blazed over and Benarbia struck the crossbar as it looked as though it could be a frustrating afternoon.
But Benarbia changed the direction of the match putting City back in front in the 78th minute following a cross from Nicolas Anelka.
Benarbia then turned provider moments later setting up Foe as the Cameroon international breezed through the Villa defence to slot home his fifth goal in his last four appearances.