|Wigan Warriors (12) 25|
|Tries: Gelling 3, Williams Goals: Smith 4 DG: 1|
|St Helens (0) 0|
Anthony Gelling scored a hat-trick as Wigan thrashed rivals St Helens - in the process ending Saints' seven-match winning run to move to within a point of securing a semi-final spot.
A fierce defensive display by Wigan and Gelling's first-half brace ensured the hosts led 12-0 at half-time.
Gelling added a third try before George Williams completed the win.
Two days after boss Keiron Cunningham insisted Saints do not want to re-sign Matty Smith, he kicked nine points.
Victory moves Wigan up to second in the table, eight points ahead of Catalans Dragons in fifth after the French side were hammered 44-0 by leaders Hull FC on Thursday.
Saints hopes of securing a home-semi final took a knock as their first league defeat since 6 June leaves them in fourth - four points behind Wigan with four Super 8s matches remaining.
Gelling powered over to edge the Warriors ahead against their near neighbours, but it was their stubborn defensive showing against a Saints side that had seven successive sets at the start inside Wigan's half which set the tone at the DW Stadium.
Stubborn in defence, Wigan remained a threat in attack, with a forward pass denying Dan Sarginson before a short ball from John Bateman allowed Gelling to punch through Saints defence untouched to score again.
James Roby went close to giving Saints the ideal start to the second half, only to be held up over the line by Frank-Paul Nuuausala.
Smith made it a three-try advantage with a drop-goal before Gelling raced away for a 100m intercept try to complete his treble and Williams went over in the final minute.
Wigan Warriors assistant coach John Winder: "It was a tough game but I thought the way we defended our own try line ultimately got us the result.
"We made plenty of errors but our mindset when we defended was top class. We leaked a few points at Castleford last week and we talked about getting back to how we defended at the start of the year and I thought we were outstanding in that area.
"We knew it was a big challenge and I thought we rose to it."
St Helens head coach Keiron Cunningham: "If you want to teach a kid how not to win, that was probably the best way to do it.
"We turned over 50% of the ball and you just can't get a foothold in the game doing that. Every time we did, we looked a little bit threatening.
"It's hard to be critical because they've been fantastic, but it's hard to stay on the crest of a wave for a long, long period and tonight we were probably a bit guilty of that."
Wigan Warriors: S Tomkins; Charnley, Gelling, Sarginson, Gildart; Williams, Smith; Crosby, Powell, Flower, Bateman, Farrell, Isa.
Replacements: Tautai, Sutton, Nuuausala, Shorrocks.
St Helens: Lomax; Owens, Fleming, Peyroux, Swift; Turner, Fages; Walmsley, Roby, Richards, Greenwood, Knowles, Wilkin.
Replacements: Amor, Vea, McCarthy-Scarsbrook, Tasi.
Referee: Ben Thaler (RFL)