On the back of their first Super League win of the year against Leeds Rhinos, Huddersfield were excellent against the unbeaten competition leaders and, at times, looked capable of causing a shock at Emerald Headingley.
Indeed, they led 12-10 at the break after a brilliant try from Darnell McIntosh just 45 seconds before the hooter.
It was the first time Super League champions Saints had trailed at half-time this season but the least Ian Watson’s Giants side deserved with the likes of Luke Yates, Adam O’Brien, Michael Lawrence and former Saint Josh Jones all in excellent form.
They had met fire with fire throughout the first period, continually matching Saints up front and playing almost error-free rugby.
Defending with energy, carrying with power, they were never daunted even if their opponents did, more often than not, make them work out from their own goalline.
However, in the second half Kristian Woolf’s side tightened their grip: it is just what they do.
When Huddersfield’s Jack Cogger saw the ball stolen from him by Mark Percival from a kick return, his team was caught offside and Lachlan Coote’s penalty levelled the game in the 46th minute.
From there, you sensed it would only go one way.
Coote and Grace led the chase to force McIntosh back five metres behind his own goalline to force another drop-out.
When Giants did have them down at their own end, back-to-back penalties for a ball steal and tip-tackle, suddenly had Watson’s men defending their own line again.
A brilliant Chris McQueen tackle denied Jonny Lomax but his side momentarily lapsed when Saints shifted left again and Wales winger Grace slalomed over from the left wing in the 53rd minute.
Coote improved before Theo Fages saw a drop goal attempt charged down by the tireless Lee Gaskell; the Frenchman did not miss when he had a second shot in the resultant set to make it 19-12.
Nevertheless, McIntosh added his second try against the run of play when Kevin Naiqama failed to claim Aidan Sezer’s crossfield kick and Sezer’s conversion reduced the deficit to just one point.
Annoyingly, though, their ill-discipline cost them again, compounding a penalty for offside by complaining about the decision and being marched back a further 10m before Grace completed his treble.
Although there was no win, it was just the sort of display Watson had demanded after they had also pushed Saints close 18-10 in the league a fortnight previously.
In the first half, he must have loved it when his prop Yates dumped Alex Walmsley with a powerful hit; that rarely happens to the England front-row.
After Saints saw another of their England internationals - Tommy Makinson - limp off after just four minutes, Giants opened the scoring soon after.
Sezer saw Saints full-back Coote had been caught up in the previous tackle and intelligently exploited the space, dabbing through a grubber for prop Lawrence to touch down with all the time in the world.
Sezer converted and the Australian scrum-half thought he had created another try in the next set when McQueen rose impressively to palm down his high kick only for referee James Child to rule Jones did not correctly ground the ball.
Saints were quickly into their groove, though, relentlessly going through their motions and it was inevitable Giants would eventually crack, Regan Grace brilliantly picking up Fages' grubber in the 17th minute.
Jones breathed a sigh of relief after dawdling trying to let a Kevin Naiqama kick run dead and almost coming unstuck.
Nevertheless, he led his side’s fine defensive effort from the resulting drop-out, Louie McCarthy-Scarsbrook eventually spilling after being repelled in front of their posts.
That said, the veteran prop had to depart for an HIA and - though no penalty was given - Child also placed Gaskell on report for a suspect challenge.
Woolf’s side did add a second try, though, when their persistent grind built towards Lomax arrowing out a pass that his England centre Mark Percival burst onto down the left.
Coote’s conversion made it 10-6 but then came Giants’ stellar second when hooker O’Brien shaped open to Sezer and Cogger but then veered blind where Kenny Edwards and Ricky Leutele brilliantly ushered McIntosh over. It would not be enough.
St Helens: Coote; Makinson, Naiqama, Percival, Grace; Lomax, Fages; Walmsley, Roby, McCarthy-Scarsbrook, Thompson, Mata’utia, Batchelor.
Huddersfield Giants: Gaskell; McGillvary, McQueen, Leutele, McIntosh; Coger, Sezwer; Yates, Cunningham, Lawrence, Edwards, Jones, Greenwood. Substitutes: English, O’Brien, Wood, Trout.
Referee: James Child (Dewsbury)
* Warrington Wolves progressed into the Challenge Cup semi-finals with a 16-6 win over Catalans Dragons.