Omari Caro and Craig Hall scored hat-tricks as Hull KR shocked Super League leaders St Helens in Chris Chester's first game in caretaker charge.
Rovers, who parted company with coach Craig Sandercock on Thursday, started strongly and went in 14-10 ahead at the break thanks to a brace from Caro.
And the hosts scored 26 unanswered points in the second half to record a comprehensive victory.
Graham Horne and Greg Eden also scored, while Travis Burns kicked four goals.
St Helens, who last won an away league game against Rovers in 2007, remain one point clear of Leeds Rhinos at the top of the table.
The home side went ahead in the sixth minute when Caro intercepted a loose pass from Jon Wilkin and sprinted down the touchline to open the scoring.
However, Saints were level four minutes later when Mark Percival capitalised on a defensive lapse to touch down after throwing Eden a dummy.
The Robins soon responded as Caro went in for his second after good work from Burns and Josh Hodgson, and Hall intercepted a pass to run in from 45 metres out, Burns converting for a 14-4 lead.
St Helens reduced the arrears just before the break, with Mose Masoe using his power to reach over the line after Sia Soliola burst through, with Percival adding the two points.
Rovers had to soak up pressure at the start of the second half, but then stunned the visitors with four tries in the space of 16 minutes to put the game out of their reach.
First, Horne took a pass on the blindside from a scrum inside his own half to run in from 60 metres out, then Eden sent Caro over in the corner as he completed his hat-trick.
Eden then set up Hall's second and third tries, first showing quick hands to feed the winger and then kicking through for him to cross.
Full-back Eden rounded off the scoring to complete a dominant performance by the hosts, who moved within a point of eighth-placed Widnes Vikings.
Hull KR caretaker coach Chris Chester:
"Of course I want the job. I loved it. But it's up to the powers that be at the end of the season.
"This is my home because I spend more time here than at my own home. From day one, the club has made me feel very welcome and it's a great family club.
"We spoke before the game about going on a journey. If we could get five results out of the last nine we could have a good crack at the play-offs.
"There's one down and we have eight to go. We have to go to Leeds on Friday with plenty of confidence."
St Helens coach Nathan Brown:
"It was a very disappointing day.
"The only positive was Mose Masoe and Louie McCarthy-Scarsbrook played well. We can't brush this one under the carpet.
"We handed them two interception tries, but Hull KR's league position is false to me.
"They've had their share of injuries and they are getting players back. That helps Travis Burns and Greg Eden get in the game."
Hull KR: Eden, Caro, Welham, D Hodgson, Hall, Burns, Keating, Netherton, J Hodgson, Weyman, Horne, Lovegrove, Ollett.
Replacements: Carlile, Larroyer, Cox, Green.
St Helens: Wellens, Makinson, Turner, Percival, Swift, Hohaia, Wilkin, Richards, Roby, Walmsley, Manu, Flanagan, Soliola.
Replacements: Masoe, McCarthy-Scarsbrook, Jones, Thompson.
Referee: James Child.