Wycombe stunned the hosts by romping into a two-goal lead after just 18 minutes; the first coming after nine minutes when Kevin Betsy found space in the area and fired home.
Nine minutes later the visitors doubled their lead, Matt Bloomfield turning past two defenders before unleashing a powerful shot which gave Andy Warrington no chance.
Rotherham pulled one back five minutes later when Johnny Mullins and Tom Pope linked up to set up Adam Le Fondre for his 12th of the season, before Nicky Law's quick free-kick was driven home from the edge of the box by Jason Taylor.
Ben Strevens restored Wycombe's lead as his curling 20 yard shot flew over Warrington, before Le Fondre netted from the spot after Chris Westwood fouled Exodus Geohaghon to restore parity after the break.
Referee Peter Quinn pointed to the spot again when, after lengthy discussions with the linesman, he harshly adjudged Mullins to have fouled Kevin Betsy, allowing Rendell to grab the winner six minutes from time in a heated contest.