Leeds were without eight players through injury and lost two more during the game, but produced a defensive performance of astonishing grit and determination.
Ash Handley would not be in the side if everyone was fit, but he has a habit of scoring tries against Saints and he delivered the goods with a second-half brace.
Jack Walker spent 80 minutes on the bench last week and five this time. He came on early after Ashton Golding was hurt in a high tackle by Zeb Taia.
Leeds scored after nine minutes. Saints have the competition’s best defence this year, but they couldn’t get to grips with Anthony Mullally who showed remarkable strength to force his way over from a few metres out, Kallum Watkins adding the extras.
The lead lasted eight minutes. Walker did really well to pick up a dangerous low kick from Jon Wilkin almost on Leeds’s line, but then Matt Parcell turned the ball over to Jonny Lomax and Saints made the opportunity count as Danny Richardson and Lomax worked the ball left to Ben Barba and the in-form full-back finished strongly at the corner. Richardson added the icing with a touchline conversion.
Barba almost scored again soon afterwards in the same spot, from Richardson’s pass, but Walker and Watkins did incredibly well to hold him up over the line.
Richardson then kicked across field and Tommy Makinson got above Ryan Hall, but knocked on as he tried to touch down, video referee Robert Hicks backing up James Child’s onfield decision of no try.
Leeds were hanging on so Saints’ decision to take the two from a penalty in front of the posts, after a ball steal by Oledzki, was a surprise and tribute to Leeds’s defence.
But they scored their second try in the set from the restart. It was a brilliantly improvised score. Ryan Hall couldn’t take Richardson’s high kick, which was batted back by Adam Swift to Richardson.
He turned the ball inside to Tommy Makinson and his final pass was finished off by Swift.
Rhinos hadn’t been able to get on the front foot since their early try, but they squared the scores with a wonderful try.
A strong run by Hall got them going forward, then Joel Moon’s pass to Tom Briscoe split the defence and with support on either side he sent Richie Myler over for the scum-half’s first Leeds try, which Watkins improved.
In the closing moments of the half Mullally was penalised in possession to give Saints a last opportunity, but a knock-on by Theo Fages kept Rhinos’ line intact.
It stayed that way until the 54th minutes. Saints again did most of the pressing, but the Briscoe-Watkins axis on Leeds’s right gave the hosts’ defence something to think about on a couple of occasions.
Leeds were coming out of their end when Walters was penalised for moving off the mark and Richardson kicked Saints back in front. Rhinos levelled again, on the hour, through a Watkins penalty goal after interference on Carl Ablett close to the line ust to the right of the posts.
Remarkably, the visitors were in front a couple of minutes later. Myler chipped a kick to Leeds’s left, Richardson got nowhere near it and the ball was picked up by Handley, though Watkins could not convert.
There was a huge moment soon after that when Parcell raced clear with Watkins and Myler in support. He turned the ball inside and the scrum-half was tackled.
Then Watkins almost got over, but was denied by a sensational tackle from Regan Grace, Barba and Lomax.
The captain was hurt and had to leave the field.
On the next play a poor pass by Briscoe was retrieved by Singleton.
He got the ball to Moon and the Rhinos stand-off jinked inside and grubbered ahead, Handley gathering to touch down again.
Myler could not land the extras and Saints got back into it with a stunning long-range try, Grace scorching clear and Barba supporting to score.
Richardson converted, but Taia knocked on from the restart and Parcell stretched over from acting-half, Myler adding the extras to secured a famous win for Leeds.
St Helens: Barba, Swift, Makinson, Percival, Grace, Lomax, Richardson, Amor, Roby, Thompson, Peyroux, Taia, Wilkin. Substitutes: Fages, McCarthy-Scarsbrook, Douglas, Lees.
Leeds Rhinos: Golding, Briscoe, Watkins, Handley, Hall, Moon, Myler, Mullally, Parcell, Singleton, Jones-Buchanan, Ablett, Delaney. Substitutes: Walker, Smith, Oledzki, Walters.
Referee: J Child (Batley).
Doncaster progressed to the fifth round of the Ladbrokes Challenge Cup after beating Newcastle Thunder 34-0 last night. The hosts’ tries came from Richard Owen, Liam Harris – who kicked five goals – Jack Sanderson, Liam Welham, Aaron Jones-Bishop and Sam Doherty.