|Leeds (2) 16|
|Tries: Hall, Cuthbertson Goals: Watkins 4|
|St Helens (8) 14|
|Tries: Lomax, Richardson Goals: Percival 3|
Leeds Rhinos saw off the soon-to-be demolished iconic South Stand with an error-strewn win over St Helens.
Saints had the better of a scrappy first-half, after Jonny Lomax crossed on the back of penalty goals apiece for both sides.
Leeds pulled clear when Adam Cuthbertson added to Ryan Hall's score.
Danny Richardson's try kept Saints hopes alive but Leeds held on and are now three points clear of third-placed Hull FC in the Super League table.
The defeat leaves Saints a point behind Wakefield, who are fourth with four Super 8s games to play.
Leeds cannot catch Castleford Tigers at the top, but are in the box seat for the second home semi-final come the top four play-offs.
Headingley's impending redevelopment meant this game was to be the last for the 86-year-old roofed terrace, and it added an emotional tinge to a match that held huge significance to the race for Old Trafford.
Unfortunately the pre-match festivities failed to transfer to the field, as neither side found their rhythm in a game high on drama but lacking in quality.
Saints' best moment of the first half produced the game's first try when Lomax latched on to Zeb Taia's pass after James Roby put the back-rower into space.
The hosts were equally disjointed but gave the crowd some cheer when a smart move to the left was finished off by Ryan Hall on his 300th club appearance.
Cuthbertson bashed his way across on the back of Leeds pressure but it was never comfortable until the hooter, particularly when the lively Richardson came off the bench to step his way across the stripe with five minutes to go.
Leeds Rhinos head coach Brian McDermott:
"I thought we were extremely good, I've never not been proud of out players although I don't say it too much. I'm proud to be their coach tonight.
"I don't know where we go the second half from, Saints were great, beating us off the deck in the first half and we never got to grips with their play-the-balls.
"We rolled up our sleeves and did some hard work, we should have executed better. It was a great game of rugby league."
St Helens head coach Justin Holbrook:
"I couldn't be prouder of my team. Unfortunately that's two weeks in a row we've been beaten by two points.
"I don't think we played poorly. We didn't have much ball in the second half, we were camped in our own half, but we got within two points away from home against a very tough side.
"We just couldn't get going for one reason or another in the second half but full credit to Leeds, they played very well."
Leeds Rhinos: Walker; Briscoe, Watkins, Sutcliffe, Hall; Moon, McGuire; Cuthbertson, Parcell, Singleton, Ward, Jones-Buchanan, Ablett
Replacements: Burrow, Delaney, Keinhorst, Mullally
St Helens: Lomax; Makinson, Morgan, Percival, Grace; Fages, Smith; Amor, Roby, Thompson, Taia, Wilkin, Knowles.
Replacements: Walmsley, McCarthy-Scarsbrook, Peyroux, Richardson