Leeds put their World Club Challenge disappointment behind them by claiming their first away win over St Helens for five years.
England winger Ryan Hall scored two tries at Langtree Park as the Super League champions atoned for last year's 46-6 hammering to leave Saints still looking for a first home win under coach Nathan Brown.
Leeds' victory, which ended a run of five consecutive away defeats by their arch rivals, was all the sweeter after overcoming the motorway closure that forced hundreds of their fans to turn back.
The Rhinos made just one change to the side that lost to Melbourne a week ago but it took them some time to settle. The match began badly for Saints when Jordan Turner put the ball out on the full from the kick-off and Leeds captain Kevin Sinfield gave his side the lead with a third-minute penalty.
St Helens were the first to demonstrate their attacking prowess, however, and full-back Jonny Lomax followed up last week's hat-trick against Bradford by scoring the game's first try, taking Jon Wilkin's pass and beating two defenders to touch down.
Gary Wheeler was unable to add the conversion and Sinfield drew his side level on 23 minutes with a second penalty, his 41st consecutive successful kick for his club, before making the break for Leeds' opening try. He dummied his way through a gap in the first line of defence and Jamie Jones-Buchanan and Danny McGuire continued the move, enabling Hall to finish at the corner for his first try.
Sinfield's failure to add the conversion ended his goalkicking run going back to September, but Leeds just about deserved their 8-4 interval lead. They went close to extending their advantage early in the second half when prop Ian Kirke burst through the Saints line but he could not ground the ball.
Leeds centre Joel Moon then demonstrated his class to carve out an opening before prop Kylie Leuluai went over for the visitors' second try. The ever-dangerous Hall was the architect, collecting McGuire's high kick and defender Louie McCarthy-Scarsbrook palmed his pass into the grateful arms of Leuluai, who forced his way over from five metres out.
Saints had lost half-back Gary Wheeler with a knee injury moments earlier and they suffered more misery when Moon produced another touch of class to set up a limping Hall for his second try.
Sinfield took his goal tally to four from five attempts to make it 20-4 but Saints finished with a flourish, with Percival capping a memorable start to his Super League career with long-range breaks which were finished off by Meli.