Bradford avenged last season's Super League Grand Final loss with a battling win over Leeds at Old Trafford.
Paul Deacon kicked the Bulls ahead after Barrie McDermott went high on Adrian Morley, but the Rhinos hit back with a try from Danny McGuire.
Deacon kicked Bradford level before Leon Pryce galloped through a big hole in the Leeds defence to make it 8-4.
Sinfield made it 8-6 before the break but a Lesley Vainikolo try and a Iestyn Harris drop-goal won it for the Bulls.
Bradford were handed the early initiative when Leeds second row Willie Poching spilled Deacon's kick-off.
And some intense early pressure led to Bulls second row Brad Meyers bursting through the Leeds defence, but he was held up over the line.
Deacon gave the Bulls the lead with a penalty on 18 minutes after McDermott went high on old team-mate Morley directly in front of the posts.
But the Rhinos hit back almost immediately, Andrew Dunemann sending through a grubber kick and McGuire pipping team-mate Ali Lauitiiti to the touchdown.
Leeds skipper Sinfield missed the straightforward conversion before Deacon made it 4-4 with a penalty on 25 minutes after Dunemann was punished for dropping the ball in the tackle.
Pryce gave the Bulls the lead on 29 minutes, spotting a gaping hole in the Leeds defence and shrugging off a Sinfield tackle to make it 8-4.
Deacon missed the extras and Sinfield made it 8-6 shortly after following some retribution by Morley, the first man to win Grand Finals in Britain and Australia, on McDermott.
It was still anyone's at half-time and it was cagey stuff after the restart until Shontayne Harpe appeared to have extended Bradford's lead on 44 minutes.
The Bulls centre pounced on a Deacon kick and bundled the ball over but Vainikolo was adjudged to have taken out Mark Calderwood.
The Rhinos had a try disallowed by the video referee six minutes later, Chev Walker losing control of the ball under the challenge of Michael Withers.
And Vainikolo extended Bradford's lead on 53 minutes, storming over after some nifty footwork from Jamie Langley before Deacon converted to make it 14-6.
On 62 minutes, Gareth Ellis made a break for Leeds before laying the ball off to Rob Burrow who was enveloped by the ubiquitous Withers.
And Deacon should have put the game beyond doubt 15 minutes from time but missed a kick after Lauitiiti aimed a slap at Morley.
However, Harris did make sure five minutes from the hooter, smashing a drop-goal straight between the posts as the Rhinos wilted.
Leeds: Mathers, Calderwood, Walker, McKenna, Bai, McGuire, Burrow, Bailey, Dunemann, Ward, Ward, Ellis, Ellis, Poching, Sinfield, Lauitiiti, Jones-Buchanan, McDermott.
Bradford: Withers, L. Pryce, B. Harris, Hape, Vainikolo, I. Harris, Deacon, Fielden, Henderson, Peacock, Peacock, Johnson, Johnson, Meyers, Radford, Morley, Vagana, Langley.
Referee: Ashley Klein (London).