|Warrington Wolves (6) 18|
|Tries: Clark, Hughes, Atkins Goals: Gidley 3|
|St Helens (12) 20|
|Tries: McCarthy-Scarsbrook, Lomax, Turner Goals: Percival 4|
St Helens survived a late Warrington fightback in the first game of the Super 8s to deny Wolves the chance to go top of the table.
Louie McCarthy-Scarsbrook and Johnny Lomax tries either side of Daryl Clark's score for Warrington put Saints 12-6 up at the the break.
Jack Hughes' try for the Wire helped them close the gap to two points.
Jordan Turner then powered over for Saints, only for Ryan Atkins to set up a nervy finish with Wolves' third try.
Warrington's Rhys Evans was denied a winner by the television match official two minutes from the end, with replays showing the winger's foot had gone into touch as he crossed in the corner.
Defeat for Warrington at the Halliwell Jones Stadium comes five days after they beat Wakefield 56-12 to book their place in the Challenge Cup final against Hull FC at Wembley.
Conversely Saints were in action for the first time in 13 days, having gone into the competition split with a 23-4 win over Wigan Warriors in the last regular season Super League game on 22 July.
St Helens' sixth successive Super league win moves them to within two points of Wigan in third.
Wolves remain a point adrift of leaders Hull FC, who host Castleford Tigers in their opening Super 8s game on Friday.
Warrington Wolves coach coach Tony Smith: "I don't want to use the short turnaround as an excuse. We were off it.
"The sharpness wasn't there. My boys tried right to the end but, if we were going to pull it out, it was going to be through individual brilliance.
"I thought St Helens were very good at getting numbers in the tackles and controlling the speed of the ruck and their kicking game better than ours. They deserved their win."
St Helens coach Keiron Cunningham: "How many Warrington games have been sat biting our nails at the end? I do think we were deserved winners.
"It was a really brave performance. In big games you've just got to find a way to win and defensively I thought we were immense.
"We started the game with zero ball and were camped on our own line and that was a common theme throughout the game.
"Sometimes you've got to win ugly games because they really count at the end.
Warrington Wolves: Ratchford; Russell, T King, Atkins, R Evans; Gidley, Sandow; Hill, Clark, Sims, Currie, Hughes, Westerman.
Replacements: Dwyer, Westwood, G. King, Wilde.
St Helens: Lomax; Owens, Peyroux, Percival, Swift; Turner, Walsh; Richards, Roby, Walmsley, McCarthy-Scarsbrook, Greenwood, Wilkin.
Replacements: Amor, Vea, Thompson, Knowles.
Referee: Phil Bentham (RFL)