Rhinos winger Mark Calderwood scored the game�s first and last tries but Saints gave as good as they got and in the end were left rueing a dreadful start in which they went 12-0 behind after nine minutes.
The Challenge Cup holders arrived only 40 minutes before kick-off after being held up in motorway traffic and were forced to apply their strapping on the coach.
They were also hit by the late withdrawal of Great Britain full-back Paul Wellens, who complained of feeling unwell on the team coach crossing the Pennines.
The disruption clearly affected the visitors, who were all at sea in the opening stages before launching a sparkling fightback in trademark fashion to enthral the 21,225 capacity crowd.
The non-stop action began as early as the second minute when the free-scoring Danny McGuire turned try-saver by intercepting Mick Higham�s pass 10 metres out from the Rhinos line.
And Saints were made to pay for a couple of handling errors by Jamie Lyon and Darren Albert deep in their own �22� as Leeds threatened a repeat of last year�s 70-0 rout.
Calderwood suddenly popped up in the left channel to take McGuire�s pass and score the first try, while centre Chev Walker touched down for the third consecutive match following a superb burst by skipper Kevin Sinfield.
Saints coach Ian Millward responded by sending on Keiron Cunningham as substitute and the change had an immediate galvanising effect.
Winger Darren Albert finished off magnificent work from late selection Ian Hardman and skipper Paul Sculthorpe on 16 minutes, and Saints were level three minutes later when Cunningham forced his way over from dummy half after the brilliant Sculthorpe had been held just short.
As play swung from end to end, Leeds loose forward Gareth Ellis reached the line only to be held up on his back, but the Rhinos regained the lead on 29 minutes when full-back Richard Mathers spun out of Lyon�s attempted tackle to touch down and Sinfield kicked his third goal.
However, Mathers turned from hero to villain four minutes later when a moment�s hesitation behind his own line proved costly, allowing Saints centre Willie Talau to follow up Jon Wilkin�s kick for an important try.
Sculthorpe�s third conversion tied the scores for a second time and the visitors, despite a 7-1 penalty count against them, could have been ahead by the break.
Scrum-half Sean Long was hauled down by Calderwood�s tackle just short of the line and Lyon got over the whitewash in stoppage time but was unable to ground the ball.
The ever-dangerous McGuire was once more the architect of the next try but this time thanks to some nifty footwork.
His 40-20 kick set up a perfect attacking position and it was from his grubber kick that substitute Willie Poching scored Leeds� fourth try.
There was simply no taking the eye off the fast and furious action as both teams demonstrated their attacking brilliance, even though it came with a high error rate.
Saints wingers Ade Gardner and Albert both dropped passes in scoring positions while, at the other end, Marcus Bai fumbled Ali Lauititi�s pass as he eyed the line.
Sinfield was off target with a drop goal attempt but Leeds finally secured their victory on 68 minutes when his kick produced a wicked bounce for Gardner and Calderwood followed up to grab the vital touch.
Sinfield maintained his 100% record by landing his fifth goal to put the seal on a memorable triumph.
Leeds: Mathers, Calderwood, Walker, Senior, Bai, Sinfield, McGuire, Bailey, Dunemann, Ward, Jones-Buchanan, McKenna, Ellis. Replacements: Burrow, McDonald, Poching, Lauitiiti.
St Helens: Albert, Gardner, Lyon, Talau, Hardman, Sculthorpe, Long, Fozzard, Higham, Anderson, Graham, Gilmour, Wilkin. Replacements: Bennett, Edmondson, Cunningham, Roby.
Leeds: (18) 30. Tries: Calderwood 2, Walker, Mathers, Poching. Goals: Sinfield 5.
St Helens: (18) 18. Tries: Albert, Cunningham, Talau. Goals: Sculthorpe 3.
Referee: Ashley Klein (London)