Super League: St Helens 12-39 Warrington Wolves
St Helens (12) 12
Tries: McDonnell, Manu Goals: Makinson 2
Warrington (23) 39
Tries: J Monaghan 2, Ratchford, M Monaghan, O'Brien, Myler, Atkins
Goals: Ratchford 4, O'Brien Drop goal: Myler
Warrington wrecked St Helens' title party with seven tries to make the hosts wait for a first League Leaders' Shield since 2008.
Saints had to avoid defeat to guarantee top spot in the Super League table but after taking a 6-0 lead, they crumbled.
Joel Monaghan scored two tries for the Wolves with Stefan Ratchford also going over and scoring four conversions.
The result means Castleford can still overtake St Helens with the regular season ending next weekend.
Cas entertain Wakefield on Sunday and play their final match next Saturday at Catalan Dragons, after Saints travel to Huddersfield the previous night.
Things looked very different in the fourth minute when Shannon McDonnell, who has broken his jaw three minutes earlier, scored a try for Saints, after being set free by Paul Wellens, and Tommy Makinson kicked the conversion.
But four minutes later, on his comeback from injury, Ratchford scored his eighth try of the season - although he missed the chance to equalise from the kick.
Road to the Grand Final - form guide
St Helens might be top of the pile but bookmakers still have reigning champions Wigan, and Leeds - five-times winners between 2007 and 2012 - ahead of them in the betting for the Super League Grand Final.
Warrington are aiming to reach Old Trafford for the third successive year, having lost 26-18 to Leeds in 2012 and then 30-16 to Wigan a year ago.
Saints last won Super League in 2006, before finishing as beaten finalists at Old Trafford five years on the trot (four times to Leeds, once to Wigan).
The match was held up for around five minutes after Wolves' Simon Grix had lengthy treatment on the pitch for what turned out to be a broken ankle.
But two minutes after play resumed, Michael Monaghan brilliantly feinted to go left before dropping his shoulder and touching down to put the visitors ahead. Warrington then scored two tries in three minutes through Gareth O'Brien and Joel Monaghan - with Ratchford converting all three to give Wolves a 22-6 lead.
Willie Manu's converted try gave Saints hope but Richie Myler kicked a drop goal just before the half-time hooter.
The hosts failed to score after the break but Myler, Joel Monaghan and Ryan Atkins, for the ninth game in a row, all went over as the home fans streamed away.
After Atkins' converted try, the League Leaders' Shield was shut away in its box and carried away from the pitch.
Saints will hope they can reopen it at the John Smith's Stadium at the end of next week.
St Helens coach Nathan Brown:
"It was not the performance we were looking for. We struggled in a few areas and their dummy-half runners caused us quite a lot of trouble.
"I can't be too critical of the guys because at the end of the day, they put the club in a good spot under a reasonable amount of adversity.
"Unfortunately we saved the off night for what could have been a great occasion for our fans but I've still got a lot of faith in the guys that we can recover from this.
"We generally recover from these losses well."
Warrington coach Tony Smith:
"It was a really good performance in many ways, particularly in the first half.
"I know they played without recognised half-backs but they are a huge team to deal with and we had to play a certain way to compete with them.
"There were three stand-outs for me. Matty Russell was sensational, Chris Hill was enormous for us and Monas [Michael Monaghan] ran the show until he got that injury.
"We're devastated for Simon Grix. I think that second half was a bit for Simon, the players spoke about that at half-time. He's had so many injuries and I think they dug in for Simon."
St Helens: McDonnell, Makinson, Dawson, Jones, Swift, Hohaia, Wellens, Amor, Roby, Walmsley, Laffranchi, McCarthy-Scarsbrook, Turner, Masoe.
Replacements: Manu for Amor (22), Masoe for Walmsley (11), Soliola for Laffranchi (22), Walmsley for Masoe (29).
Warrington: Russell, J. Monaghan, Atkins, Ratchford, R. Evans, O'Brien, Myler, Hill, M. Monaghan, Harrison, Laithwaite, Westwood, Grix.
Replacements: Higham for Harrison (28), Currie for Westwood (46).
Substitutes: Asotasi, Waterhouse.
Referee: James Child (RFL).