Former Huddersfield coach Nathan Brown had the chance to hand the shield to his old club but his St Helens side never fully recovered from an appalling start in which they trailed 22-0 after 24 minutes.
They produced a gritty fightback, inspired by overseas duo Willie Manu and Tony Puletua, but it was not enough to prevent a first defeat in six matches.
The Giants will still secure the trophy with one win from their last two matches, starting with the visit of Wakefield to the John Smith's Stadium on Sunday, but at least Warrington made sure of a top-three finish for the fourth year in a row.
Wolves coach Tony Smith opted against playing scrum-half Gareth O'Brien following his return from a loan spell at Saints and his choice of the versatile Simon Grix proved a masterstroke as he revelled in the role.
The visitors were also boosted by the return of veterans Adrian Morley, Lee Briers and Garreth Carvell, while young centre Rhys Evans was a tryscorer on his first Super League outing for five months.
Warrington had suffered a shock home defeat by Widnes in their previous match and they looked determined to make amends from the start.
Briers made his mark after just three minutes, producing a lofted kick of pinpoint accuracy for winger Joel Monaghan to score his 23rd Super League try of the season.
Two minutes later a storming break from deep inside his own half set up the position for Grix to get Evans over and Stefan Ratchford's goal made it 10-0.
Saints struggled to get out of their own half at that stage and Warrington tightened their grip when full-back Jonny Lomax failed to cope with Briers' grubber kick, losing the ball in the tackle by Mick Higham, who was left with the simple task of touching down.
With Ratchford's second making it 16-0, Brown's response was to send on his captain Paul Wellens but his side fell further behind on 24 minutes when Grix's grubber kick caused more confusion in their defence, gifting a try to second rower Trent Waterhouse.
At 22-0, it was beginning to look ugly for the home side but centre Jordan Turner took Jon Wilkin's pass to power his way over for a try and winger Adam Swift added another just before half-time after smart approach work from Wilkin and Lomax, and a clinical final pass from Francis Meli.
The scores injected fresh confidence into St Helens, who dominated the opening exchanges of the second half.
Lance Hohaia, who moved into the hooking role, twice got over the line only to be held up each time but the pressure paid off on 55 minutes when a superb offload from second rower Manu enabled Lomax to cross for his side's third try.
Lomax kicked his second goal from the touchline to cut the gap to just six points but Briers calmed the Wolves' nerves with a drop goal on 65 minutes and Carvell made sure of the win with a last-minute try, with Ratchford adding the extras.
A late try by Danny McGuire on his return from a broken leg helped Leeds get back to winning ways as they edged out a committed Catalan side 20-12 in a tight contest.
A clever run by Ryan Hall allowed Leeds to open the scoring after a cagey first half-hour, and Kevin Sinfield converted before he added a penalty goal for an 8-0 lead for the hosts at the break.
In the second period Catalan hit back when Lopini Paea crossed and another score by Olivier Elima gave the visitors a second-half lead, but Mitch Achurch's fine try saw Leeds regain the lead, and McGuire sealed the win after touching down Sinfield's clever kick.
Leeds welcomed back McGuire as he made his first appearance since breaking his leg in May.
Forward Ryan Bailey returned but Rob Burrow missed out due to a back injury.
Sydney Roosters-bound prop Remi Casty returned for Catalan after he missed the home win against Wigan through injury.
Immediately from the restart the home side showed their intent by collecting the ball from their own kick-off.
However, any momentum was lost when Bailey knocked on.
The Dragons turned the screw straight away as Ian Henderson broke down the blindside, but he did not choose the right option and Thomas Bosc was brought down and subsequently lost possession.
Both sides were showing a willingness to throw the ball around in their own half, but a wonderful passing move for the Dragons was halted when Damien Blanch kicked aimlessly ahead.
In the 26th minute, following an error by the Dragons, tempers flared and as a result Leeds' Bailey and the Dragons' Blanch were sin-binned by referee Phil Bentham.
One minute later Hall showed his intelligence by exposing the blindside in Blanch's absence, and he raced down the side-line from dummy-half and stepped inside Catalan's Brent Webb for the opening score.
Sinfield converted, and on the back of an epic run by Joel Moon, the Leeds' captain added a penalty goal before the break despite receiving a knock to his shoulder.
At the start of the second half Vincent Duport earned his side great field position after a penalty.
Camped on the Rhinos' line, Scott Dureau provided an excellent short pass for Paea to cross after he rounded Leeds' Zak Hardaker with some neat footwork.
Bosc reduced Leeds' lead to two points with the conversion, but Leeds regained the momentum and went close when Brad Singleton was held up.
However, Elima barged over from close range for Catalan moments later to give the French side the lead as he exposed some poor defence by the hosts, before Bosc converted for a four-point Dragons' lead.
An Elliott Whitehead interception had the Dragons on their way again, and when Leeds were penalised Bosc had a chance to extend the visitors' lead, but he missed the penalty goal.
Leeds dominated a frantic period of the game late on and they punished the French side with eight minutes remaining when Liam Sutcliffe sent Achurch on his way as the big prop raced through to score.
Sinfield converted to give the home side the lead, and he created McGuire's late score which sealed the win.
Daniel Holdsworth gained a measure of revenge for Hull's defeat to Wigan in the Challenge Cup final last weekend as the Black and Whites claimed a last-second 34-33 win.
The visitors led 12-6 thanks to tries from Jason Crookes and Tom Briscoe, with Andy Powell's first try in rugby league sandwiched in the middle, but Ben Flower and Ryan Hampshire crossed in the closing stages of the first half to give the Warriors a 16-12 interval lead.
The second half was end to end with Wigan leading 26-12 at one stage with tries from Joe Burgess and Iain Thornley but Hull refused to lie down and hit back with three scores to level it up at 26-26.
Anthony Gelling and Briscoe then traded scores and although Sam Powell dropped a goal, two from Daniel Holdsworth in the dying minutes sealed it for Hull.
The Warriors were missing a number of key personnel with coach Shaun Wane resting no fewer than 11 of his Wembley heroes, meaning youngsters like Hampshire, Powell, Burgess, Lewis Tierney and Dominic Manfredi got the chance to impress ahead of the play-offs.
Hull also made a number of changes from the Challenge Cup defeat with Andy Lynch, Gareth Ellis and Mark O'Meley absent, while talented hooker Aaron Heremaia was suspended.
It was Hull who struck first when winger Crookes used his strength to beat Burgess in the corner to put the visitors in front.
However, the roof almost came off the place in the 22nd minute when rugby union convert Powell crossed for his first try in league to make it 6-6.
It did not take long for Hull to recapture the lead when Jacob Miller and Holdsworth combined to send England international Briscoe in at the corner, Danny Tickle again converting to put the visitors 12-6 ahead.
Two tries in two scintillating minutes saw Wigan go from 12-6 down to 16-12 up. First, Flower crashed over from close range seconds after being held up over the line and straight from the kick-off, Gelling broke down the right and sent Hampshire racing away.
Wigan looked unstoppable and crossed for their fourth try of the game when Thornley finally offloaded to his winger and Burgess was on hand to score his first try for the Warriors.
Thornley himself touched down to put Wigan 26-12 ahead before Hull then did to Wigan what the Warriors had done in the first half by crossing for two quick scores.