The Hoops interim boss had claimed his side were the best in the country heading into the last 16 tie despite Rangers clinching the Scottish Premiership title with a 20 point lead at the top of the table.
Rangers star Borna Barisic hit back at the “disrespectful” comments, and Kennedy clarified his claims, stating that he felt Celtic could be the best “on their day” and that he fancied his side’s chances of defeating their Glasgow rivals.
However, first half goals from Steven Davis and Ryan Kent secured a 2-0 win for the Ibrox side, with Allan McGregor also saving a late penalty from Odsonne Edouard.
And Rangers wasted no time in reminding Kennedy of his remarks with a pointed post-match tweet, stating: “A win against the best team in the league.”
Rangers will now meet St Johnstone in the quarter-final next weekend.