Hull FC (12) 14
Tries: Briscoe, Washbrook Goals: Tickle 2, Fitzgibbon
Leeds (0) 18
Tries: Donald, McGuire 2 Goals: Sinfield 3
Danny McGuire finishes Leeds' joint top Super League try scorer with 23
Two late Danny McGuire tries at the KC Stadium helped Leeds come from behind to seal fourth place and set up a play-off showdown next Sunday against Wigan.
Despite prop Lee Radford's sending off early on, Hull shocked Leeds by taking a 12-0 half-time lead thanks to tries from Tom Briscoe and Danny Washbrook.
Scott Donald pulled one back, only for Craig Fitzgibbon's boot to put 12-man Hull 14-6 up with 15 minutes left.
But McGuire conjured up some magic with two match-turning tries in six minutes.
Hull not only missed out on fourth spot, but actually slipped a place in the table to sixth, thanks to Huddersfield's win over Catalans in Perpignan - and that sets up a play-off derby for the Black and Whites at the KC Stadium next Saturday (1800 BST) against their neighbours, seventh-placed Hull KR.
Leeds, by contrast, get an extra day off before having to go to Wigan on Sunday evening (1845 BST) - a game put back almost 48 hours due to Wigan Athletic having use of the DW Stadium for a Premier League game against Sunderland on the Saturday afternoon.
But Leeds might so easily not have made the top four.
The defending Super League champions looked to be suffering from a Wembley hangover from last weekend's 30-6 Challenge Cup final mauling by Warrington - and thye were still trailing with 10 minutes to go.
But the effects of playing most of the match a man short following the hot-headed Radford's dismissal eventually caught up with Hull.
Just nine minutes had gone when a sudden rush of blood to the head earned a straight red card for Hull club captain Radford, who only this week pledged his future to the club by signing a new two-year contract.
He took exception to apparent use of the elbow by Leeds prop Ryan Bailey and began swinging punches which did not miss their target.
Referee Ian Smith, a late replacement for a sick Phil Bentham, decided to send him off, while Bailey ended up in the blood bin and was roundly booed on his return.
Hull, with first-choice half-backs Sean Long and Richard Horne in tandem for only the fifth time this year, looked the more organised team in the first half.
Even before the dismissal, the game had been open with Hull stand-off Horne and McGuire producing clean breaks that prompted some desperate defence but it took 22 minutes for the first score.
An offload from the tackle by centre Kirk Yeaman created space on the right and England international Briscoe came off his wing to beat three defenders on a superb run to the line.
Keith Senior made a surprise switch to the Leeds pack, starting at second row
The score appeared to knock the early confidence from the champions, Hull doubling their lead eight minutes before the break when Long and Fitzgibbon combined cleverly to get substitute Washbrook racing away to the line.
Danny Tickle converted both tries to make it 12-0 but the Leeds fightback began just three minutes into the second half when Hull put themselves under pressure by conceding back-to-back penalties.
Leeds finally made both the pressure and their man advantage pay when Rob Burrow's cut-out pass gave recalled winger Donald a clear run to the line.
Kevin Sinfield's touchline conversion made it 12-6 and Leeds ought to have been level when centre Lee Smith breached the Hull line but slow motion replays indicated a knock-on as he attempted to ground the ball.
As at Wembley, panic set in among the Rhinos ranks and there was clear frustration on the hour when they disputed referee Smith's decision to award a penalty for ball-stealing.
Fitzgibbon punished the error with a penalty to put the home side two scores in front again but the deficit was back to just two points when a break from Burrow set up half-back partner McGuire to jink his way over for a second Leeds try which Sinfield converted.
The game was finely balanced when Donald pulled off a timely interception to break up a threatening Hull attack and Leeds went up field to score the winning try through that man McGuire, whose brilliant footwork undid the hosts' defence.
McGuire's two tries took him level with Ryan Hall on 23 as Leeds' top Super League scorer this season.
The Rugby Football League's match commissioner revealed afterwards that he would be incorporating in his report an incident in which a spectator ran onto the field during the later stages and grabbed Leeds winger Donald.
Hull coach Richard Agar said:
"Lee Radford is gutted and has apologised to the boys. He copped two beauties on the side of his head and reacted.
"Nine minutes into the game, the referee could have showed a little bit of common sense. We had two front rowers going at it hammer and tongs and two sin-binnings might have defused the situation.
"I'm disappointed for our guys that a decision like that ultimately cost us. It was probably the difference between the two sides.
"Fatigue probably got the better of us. We got caught defensively purely and simply because we were down on numbers."
Leeds coach Brian McClennan said:
"You just can't punch players for no reason at all.
"It was very eventful. There was a lot at stake for both teams and, because of that, there was also a lot of passion.
"It was quite a dramatic match in a lot of ways and not just football. It was a match I'll never forget.
"We've no complaints against Hull. You employ a security firm and that security firm is going to have to answer some pretty serious questions."
Hull: Hall, T Briscoe, Berrigan, Yeaman, Lyne, Horne, Long, Radford, Houghton, O'Meley, Manu, Tickle, Fitzgibbon.
Replacements: Moa, Washbrook, Cusack, Turner.
Leeds: Webb, Hall, Delaney, Smith, Donald, McGuire, Burrow, Leuluai, Buderus, Bailey, Ablett, Senior, Sinfield.
Replacements: Diskin, Eastwood, Kirke, Lauitiiti.
Referee: Ian Smith (Oldham).