A quiet opening quarter saw just the one score as Blair Walsh kicked a 52-yard field goal to ensure that the Vikings came away from their opening drive with points on the board.
Walsh added another three points early in the second quarter before the first touchdown of the match came shortly before half time.
The Rams finally got onto the scoreboard in the third quarter as Greg Zuerlein converted a 56-yard field goal to reduce the deficit to 10 points.
However, the Vikings put themselves in complete control of the match with just over two minutes remaining in the third quarter as Cordarrelle Patterson shrugged off a number of tackles to complete a sensational 67-yard score.
The visitors all but sealed the victory in the fourth quarter as they scored their third touchdown of the match, this time Cassel picking out Kyle Rudolph in the endzone with a seven-yard pass.
If there was any remaining doubt, that was well and truly put to bed with just over three minutes remaining as Harrison Smith intercepted a pass before racing through for an 81-yard touchdown.
Zuerlein added a late 46-yard field goal for the Rams, but it was far too little too late as the Vikings eased to the win.