Leeds skipper Kevin Sinfield scored his 3,000th point for the club, but St Helens put a dampener on his celebrations by claiming a 31-18 victory at Headingley on Monday night to complete a Stobart Super League double.
Scrum-half Jonny Lomax scored two of his side's five tries as Saints bounced back from their Challenge Cup exit at the hands of arch rivals Wigan to inflict more misery on their 2011 Grand Final conquerors.
Leeds twice held the lead as they attempted to avenge their 46-6 defeat at Langtree Park in March, but St Helens produced a strong finish to secure the points and leave their rivals trailing in eighth place at the half-way stage of the regular season.
Jon Wilkin, Tom Makinson and Paul Wellens scored the other tries for St Helens while Brett Delaney, Jamie Jones-Buchanan and Danny McGuire crossed for Leeds.
