Brilliant Leon Pryce masterminded Leeds Rhinos' first engage Super League defeat of the season - as St Helens began to heal the hurt of successive Grand Final defeats.
Matt Gidley started and finished Saints' try scoring as the champions lost for the first time in six league starts.
Pryce was unstoppable as rugby league's greatest grudge match erupted into second-half violence.
It was more luck than referee Phil Bentham's handling of the game that both teams finished with 13 men.
Ryan Bailey's tackle that ended Maure Fa'asavalu's game after 47 minutes may yet end in a disciplinary hearing.
And Mr Bentham also declined to punish Saints' Lee Gilmour and last season's Old Trafford man of the match Lee Smith for a punch-up.
Leeds' only consolation was a landmark try for Keith Senior and a last-second conversion to Senior's second try by Kevin Sinfield that keeps Brian McClennan's team on top of the table.
Evergreen Senior joined Saints' hooker Keiron Cunningham as the only players to score a try every season since Super League started in 1996. But the bald centre's double was of little consolation to the visitors.
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