St Helens kicked off the Super League Super 8s with a fine 26-12 victory at leaders Castleford.
Castleford tries: Milner (48), Monaghan (72)
Goals: Gale (48,72)
St Helens tries: Taia (17), Roby (54,75), Lomax (67)
Goals: Percival (17,22,54,67,75)
St Helens condemned Super League leaders Castleford to their first home loss in more than a year as they underlined their own title credentials with an impressive victory.
Not since Warrington won at Wheldon Road in July 2016 had Daryl Powell's men tasted defeat on their own turf but resurgent Saints showed their mettle to win the Super 8s opener.
Tries from Zeb Taia, James Roby (two) and Jonny Lomax clinched the win for a St Helens side who continue to show significant improvement under Australian head coach Justin Holbrook.
Castleford remain overwhelming favourites to secure the League Leaders' Shield but Saints moved ominously into the top four with this win as they eye another charge towards Old Trafford.
Castleford were boosted by the return of forward Oliver Holmes for his first appearance since April after a knee injury.
Saints scrum-half Matty Smith made his comeback from a nasty eye injury sustained against Leeds in June.
Both players started on the bench and the visitors were looking to make amends for their two previous defeats at Wheldon Road earlier this season.
Thumped 53-10 in the Challenge Cup on May 13, Saints lost again during the regular Super League season three weeks later.
Chances were scarce during the opening quarter of the match until the visitors opened the scoring in the 17th minute.
Roby found Theo Fages and the Frenchman found Taia advancing at pace inside the left channel.
Taia had too much strength for the Castleford defence as he brushed past Zak Hardaker and charged over the line for a try which Mark Percival converted.
England centre Percival then added a penalty soon after before Saints were denied a second try when replacement prop Kyle Amor grounded the ball from a high kick, but Ryan Morgan was deemed to have knocked the ball forward and Castleford survived.
The Tigers then saw a try ruled out when Jy Hitchcox grounded the ball from Greg Minikin but the score was disallowed for offside.
Saints therefore led 8-0 at the break but Castleford upped the tempo after the restart and, after back-to-back penalties, Adam Milner barrelled under the posts from dummy half to score in the 48th minute.
Luke Gale converted to cut St Helens' lead to two points but Saints then conjured a try which typified their attacking principles.
Morgan Knowles and Luke Thompson combined to send Fages breaking clear inside the left channel, and although the Frenchman was tackled 10 metres out, a quick pass from Lomax sent Roby diving under the posts.
Percival's conversion made it 14-6 and Saints dug deep to protect their hard-earned advantage before grabbing a third when Lomax pounced to ground a clever kick from Smith and Percival added the extras.
Joel Monaghan's acrobatic effort in the right corner gave Castleford a flicker of hope but Roby barrelled over late on for his second and Percival booted his fifth goal.
St Helens boss Justin Holbrook: "It was always going to be a tough game, we knew that and we expected it, so to come here tonight and get the win, I couldn't be happier.
"No matter how much homework you do, Castleford are still a very dangerous side and it was up to our boys to continually make the right decisions in defence.
"We did that and it was really pleasing, plus James Roby is as a good a nine as I've seen.
"He's not just tough and creative, he's also fit, and he's a great guy.
"He loves playing rugby league and they are the type of players you need when you have a tough assignment like we had tonight.
"He was fantastic and I've been happy with how we're playing and training. I think we're getting better, that's for sure."
Castleford boss Daryl Powell: "I don't think there was much between the teams, but they defended pretty well and there were some key turning points in the game.
"It was pretty tight leading up to half-time, but I thought Saints played really well and I expected them to.
"We haven't had this feeling for a fair while, but I think it will probably help us moving down the track.
"Our effort was fantastic and the intensity of the game was great but they were the better side.
"I just said to the boys 'I think we will learn from this' and it could help us.'"