Leeds to face Wigan in Grand Final on 10 October
Leeds Rhinos chasing domestic treble
Roby scored St Helens' opener, Hardaker responded
Walsh drop-goal and Percival try put Saints 13-8 up
Hall and Watkins completed Leeds comeback
St Helens fail to get over the line with an attacking set.
It's Jamie Peacock who brings down James Roby on the last tackle. His career will be over in 14 minutes' time, unless the Rhinos can find a way back into this one.
For all money, St Helens looked as if they were about to crack before that try from Mark Percival.
Their bodies are battered and bruised, but they've defended like champions at Headingley.
Their title defence remains alive.
Leeds Rhinos 8-13 St Helens
Is that the moment or what?! Mark Percival scores for St Helens, who take a giant leap towards Old Trafford.
The video referee deems that Ryan Hall dropped the ball, rather than it being stolen, and Saints profit from it to score through Percival out wide.
He probably wouldn't have been out there if Tommy Makinson hadn't gone off injured.
Luke Walsh's unsuccessful kick from the touchline is crucial - it means Leeds can win with a converted try.
As Leeds give away a penalty of their own deep in St Helens territory, my mind is being drawn back to 2013 and a play-off tie between these two teams.
It was just like this - mightily close - before Danny McGuire's drop-goal sealed a one-point win.
One feels it's going to be something similar that settles this one tonight.
Leeds Rhinos 8-9 St Helens
Ray French
BBC Radio Merseyside
Quote MessageIt's absolutely balanced. Both teams are going at it hammer and tongs. Something has got to give shortly.
Jon Wilkin puts a massive kick in the air and the kick-chase from his St Helens team-mates is very, very lethargic.
Perhaps a signal of the huge effort they've put in so far this evening.
As Leeds bring the ball back, they win a penalty.
What a break by Kyle Amor for St Helens, out of nowhere!
He has support but goes himself and is tackled close to the try-line by Zak Hardaker.
Leeds escape with a goal-line drop-out, giving Saints another chance to run at the Rhinos. The chance goes begging, though, as Joe Greenwood drops the ball.
Leeds Rhinos 8-9 St Helens
Image source, Getty ImagesLeeds centre Kallum Watkins has been one of the stars of the Super League season, and he's nearing a personal milestone.
Can he reach it tonight and send the Rhinos to Old Trafford, keeping alive those treble hopes?
That's it for St Helens winger Tommy Makinson, he's admitted defeat in his battle with injury.
As Makinson hobbles off, BBC 5 live sports extra commentator Stuart Pyke thinks Mark Percival will be heading out to the wing and Louie McCarthy-Scarsbrook will be in the centres alongside Josh Jones.
Leeds Rhinos 8-9 St Helens
Ray French
BBC Radio Merseyside
Quote MessageIs that a let-off for St Helens or good judgement? It is another life for the Saints.
Leeds Rhinos 8-9 St Helens
St Helens don't make much ground with their set of six and back come Leeds, who think they may have scored through Carl Ablett...
On-field official Robert Hicks signals "try" when referring up to the video referee.
But the video referee disagrees. Two more tackles of the set to go...
And St Helens survive. Wow. What a passage of play.
St Helens end their set of six with a low kick, which is easily gathered and sent wide to Ryan Hall, who gallops clear - reminiscent of his match-winning try at Huddersfield last week.
Saints full-back Adam Quinlan somehow tracks back to stop the winger.
Leeds huff and puff but they can't blow the Saints wall down, as the visitors defend like champions to keep the Rhinos out.
A superb kick by St Helens captain Jon Wilkin holds up on the Leeds try-line and gets the Rhinos scrambling back. Zak Hardaker survives once, but not twice, and is tackled in goal.
Leeds have a drop-out. Chance for the visitors.
Danny McGuire tests out Tommy Makinson with a high kick and the Saints man takes it very, very gingerly. I'll be surprised if he's on the field for too much longer.
Tommy Makinson is clearly struggling with what looks like an ankle knock. St Helens have no backs in reserve. If he can't continue, not only will he be a huge loss, but also it will leave head coach Keiron Cunningham with some thinking to do.
Leeds Rhinos 8-9 St Helens
St Helens, for whom a limping Tommy Makinson has appeared for the second half, kick us off.
#bbcrl
Comedian Johnny Vegas is cheering his beloved St Helens on from afar - will he see his side book a Grand Final spot?
Stick with us to find out...
HT: Leeds Rhinos 8-9 St Helens
Brian Noble
Former Great Britain coach, BBC 5 live sports extra
Quote MessageSaints started the strongest, I thought they looked really composed and caught Leeds cold. In the middle part of the half, Leeds looked stronger, they pounded Saints’ line, they got over the line, they created opportunities and created kicks and made breaks. It is an end-to-end classic.
Live text and radio commentary on BBC Sport
We're just eight days away from one of the biggest days in the rugby league calendar - Super League's Grand Final at Old Trafford.
Image source, SWPIX.COMEither Leeds Rhinos or St Helens will face Wigan Warriors, with the winners being crowned Super League champions.
Kick-off is at 18:00 BST on Saturday, 10 October.
We'll bring you live text commentary on the BBC Sport website, starting at 17:00 BST, while BBC Radio 5 live, 5 live sports extra and BBC local radio will also provide coverage.
BBC Two will screen highlights of the Grand Final on Sunday, 11 October at 17:00 BST.
Sunday: Brisbane Broncos v North Queensland Cowboys (09:15 BST)
Image source, Getty ImagesDown under, the Australian rugby league public already know their Grand Finalists for 2015.
Brisbane Broncos face North Queensland Cowboys in Sunday's NRL Grand Final.
Cowboys and Australia half-back Johnathan Thurston won a record fourth Dally M medal - the award given to the NRL's best player - earlier this week. He is hoping to lead his side to their first ever Grand Final success.
BBC 5 live sports extra will join ABC in Australia for live commentary from Sydney at 09:10 BST.