Saints – who a fortnight ago lifted the Powergen Challenge Cup – secured the League Leaders’ Shield with this win and now look odds on to complete the set with a Grand Final win at Old Trafford next month.
Jamie Lyon provided the inspiration for the home side by claiming a hat-trick in the opening twenty six minutes; with Francis Meli, Sean Long and Ade Gardner also touching down for a 30-0 half time advantage.
Paul Wellens grabbed a brace in the second forty with Meli and Gardner each scoring a second time to complete the rout.
Lyon – who will return down under at the end of the season – also added six goals to the total, but could not compete with Paul Anderson’s jaw-dropping effort from the touchline.
"When they get in that mood, they are irresistible. We played very well but I don't know how much was riding on the game” said Anderson.
"We have got two legs of a treble and we will celebrate the reward for our hard work but we will knuckle down for the rest of the season.
"It was a very skilful performance from a very hungry and motivated group of players."
Shell-shocked Leeds coach Tony Smith blamed the heavy loss on his side’s slow start to the game, allowing the Saints to take control early on.
Smith said: "We gifted them a start and you can't do that. They were white-hot for long periods and momentum is a difficult thing to stop when you've got a team as formidable as Saints.
"I thought we started to build a game in the second half but we needed to do that from the start. We are hurting a bit, obviously, but you have days like that.
"Sometimes everything you touch turns to gold, tonight everything turned to coal."