Josh Charnley scored Leigh's first try and celebrated by signing a new contract
Tries: Charnley, Armstrong, Hanley 2, Cook, Ipape, Alick-Wiencke, Mulhern Goals: Cook 8
Leigh Leopards secured their place in Super League's top six by thrashing St Helens, who will now not appear in the play-offs for the first time in the Super League era.
Saints' hopes of protecting their unblemished record were ended by an ignominious defeat as Leigh ran in eight tries.
Tries from Josh Charnley, David Armstrong, Umyla Hanley and Adam Cook opened up a 24-10 half-time lead, with Jacob Douglas and Tristan Sailor replying for Saints.
After half-time, Mark Percival was sin-binned for Saints before Edwin Ipape extended Leigh's lead, Hanley scored his second try and Jacob Alick-Wiencke and Robbie Mulhern also crossed.
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Victory secured Leigh's place in the play-offs for the fourth consecutive season and kept them fifth in the table. They could yet move up to fourth, above Wakefield, after next week's final round of fixtures.
It took them 10 minutes to score the first try as Saints failed to deal with Cook's kick, which fell for Leigh to spread the ball for Charnley to walk in on the right wing.
He then celebrated by signing a mock contract and, moments later, the public address confirmed he had signed a new deal for the 2027 season.
Leigh scored a second try four minutes later as Armstrong, Cook and Lachlan Lam combined from deep in their own half to break up the left before Armstrong sprinted in from halfway.
Saints responded by working space for Douglas to go over in the right corner before phenomenal feet from Harry Robertson left the defence for dead and he sent Sailor under the posts.
But Robertson then missed a tackle that allowed Innes Senior to break for Leigh and create Hanley's first try, before Ipape drove for the line, his offload went to ground but Cook grubbered in-goal and touched down.
After half-time, St Helens blew a two-on-one on the left wing before they lost Percival – who recently announced he will retire at the end of the season – to the sin bin for a high tackle.
