|Catalans (12) 22|
|Tries: Mead, Casty, Thornley, Edwards Goals: Drinkwater 3|
|St Helens (14) 26|
|Tries: Percival, Fages, Lomax, Knowles Goals: Richardson 5|
St Helens all but sealed the League Leaders' Shield ahead of rivals Wigan Warriors, but left it late to beat Catalans Dragons in a pulsating game.
Morgan Knowles' score in the final minute ensured a six-point gap on Wigan with a superior points difference and only three games left to play.
Saints had trailed 22-20 before that score after Catalans overhauled a 14-12 half-time deficit to lead.
However, Knowles crossed and Danny Richardson kicked the goal to seal it.
The defeat was doubly painful for Catalans, who saw Samisoni Langi sidelined through injury and Julian Bousquet split his nose in a head-to-head collision.
Having had their Challenge Cup final hopes ended by Catalans, Saints had extra motivation to come up with the points in Perpignan in a bid to overcome their derby thrashing by Wigan last time out.
This was Catalans' first home game since lifting the Challenge Cup at Wembley, and in front of a partisan crowd, the Dragons - winless so far in the Super 8s - made a flying start.
David Mead crossed from close range and Remi Casty profited from some smart offloading to score a second.
Saints responded, and Mark Percival and Theo Fages scores put them in position going into the break.
Desperate to break their duck, Catalans were defiant and lifted their game after half-time, adding further tries from Iain Thornley and Kenny Edwards on the left edge to give their fans hope.
Saints rallied, and were denied by the video referee before Jonny Lomax scored, and Knowles' late heroics left Catalans deflated and the trophy-bound visitors elated.
Catalans Dragons: Gigot; Tierney, Mead, Wiliame, Thornley; Langi, Drinkwater; Simon, McIlorum, Moa, Bird, Edwards, Casty.
Replacements: Bousquet, Baitieri, Da Costa, Goudemand.
St Helens: Lomax; Makinson, Costello, Percival, Grace; Fages, Richardson; Amor, Knowles, Thompson, Taia, McCarthy-Scarsbrook, Wilkin.
Replacements: Douglas, Lees, Ashworth, A. Smith.
Referee: Liam Moore (RFL)