St Helens took advantage of the first-half dismissal of Leeds centre Joel Moon to earn a precious win that takes them a step closer to securing top spot in the First Utility Super League.
The Challenge Cup winners were forced to play for an hour with 12 men after centre Moon was sent off by referee Richard Silverwood midway through the first half for an illegal shoulder charge on St Helens centre Mark Percival, who had to be substituted.
With skipper Kevin Sinfield and stalwart Jamie Peacock at the heart of a superb defensive effort, the Rhinos looked capable of hanging on but the task proved beyond them as Saints came from 12-2 down to snatch a 13-12 victory that takes them five points clear of nearest rivals Wigan.
Stand-off Lance Hohaia was St Helens' hero on his return to the side with a drop goal seven minutes from the end which followed two quick tries against a tiring Leeds defence by Louie McCarthy-Scarsbrook and James Roby.
Now only Castleford can prevent Nathan Brown's men from clinching the league leaders' shield but they will need to win their last three games and hope Saints slip up in both their last two.
Leeds, who were without two of their Cup final heroes, Danny McGuire and Rob Burrow because of injury, have now lost three successive league matches to take some of the shine off their Wembley triumph.
Saints took the lead with a fifth-minute penalty goal from Percival but then spent most of the first half on defence.
With hooker Paul Aiton revelling in his rare opportunity to start a match and Peacock and Jamie Jones-Buchanan tearing into the Saints defence, the home side were full of attacking threats and that did not change even when they were reduced to 12 men with Moon shown a red card for his ugly challenge on Percival.
Sinfield kicked his side into a 4-2 lead with a couple of penalties and the Rhinos scored the only try of the first half on 29 minutes when Brett Delaney's probing run stretched the St Helens defence and half-back Liam Sutcliffe went past a wrong-footed McCarthy-Scarsbrook to touch down.
Sinfield's conversion made it 10-2 and he added another two points with a third penalty on the stroke of half-time.
Saints rarely threatened and when a break out of defence from winger Tom Makinson eventually set up a promising position for them, they failed to make the most of it when Jordan Turner got in the way of team-mate Willie Manu's dash for the line.
The visitors improved dramatically in the second half, with full-back Shannon McDonnell making an impact on attack in his second appearance for the club.
Leeds defended magnificently, though, and Sinfield temporarily relieved the pressure with his first 40-20 kick of the season.
However, the momentum was firmly with Saints and it was no surprise when they eventually prized open the home side's defence, with Hohia putting McCarthy-Scarsbrook through a gap for a try on 62 minutes.
Turner fluffed the comparatively easy goal-kick but Makinson was on target seven minutes later to convert Roby's try from dummy half to tie the scores and Hohaia kept his nerve to land the all-important drop goal.