Leeds ran in 12 tries against Widnes to secure a high-scoring victory.
Ryan Bailey, Ryan Hall (2), Shaun Lunt, Zak Hardaker, Richard Moore and Brett Delaney all went over for Leeds with Stefan Marsh and Frank Winterstein scoring for Widnes in the first half.
Cameron Phelps and Marsh again gave the visitors the merest glimmer of hope but it was not to last.
Darrell Griffin, Kylie Leuluai, Stevie Ward, Hardaker and Jimmy Keinhorst all scored to give the hosts the win.
Despite the convincing nature of the win it was not an entirely happy night for Leeds who lost Danny McGuire to a knee injury that boss Brian McDermott told BBC Radio Leeds he fears could see him miss the Challenge Cup final.
McDermott rested Jamie Peacock, Jamie Jones-Buchanan and Rob Burrow for the visit of the second from bottom Vikings.
It did not take long for the Rhinos to go ahead, Bailey powering over to leave Sinfield with an early kick, on a night where he was successful with 10 of his 12 attempts.
McGuire and Carl Ablett teed up Hall's first before Lunt crashed over after McGuire was held up inches from the line, as he looked for his record-breaking 200th Super League try.
Marsh went through the Rhinos defence to put Widnes on the board only for Hardaker, Moore and Hall to all go over for the in-form hosts.
Winterstein got the Vikings' second score only for Delaney to re-assert the Challenge Cup finalists' dominance before the interval.
Quick-fire tries from Phelps and Marsh made the scoreline look temporarily respectable before Leeds launched a stunning five-try salvo.
Griffin, Leuluai, Ward, Hardaker and a first ever Super League try for Keinhorst put some gloss on the victory for the hosts.
Leeds travel to Catalan Dragons next week for the final match before the showpiece against Wigan at Wembley on 25 August.
Their victory means they are assured of a place in the play-offs while Widnes remain just two points above bottom side London.
VIEWS FROM THE DRESSING ROOM
Leeds coach Brian McDermott:
(On McGuire's injury) "It could be just a bang or it could be a big one - a twist and maybe ligament damage, so it is concerning.
"My heart goes out to him if it is ligaments, but we hope it is just sore.
"We will leave it until the 11th hour because of what he means to us. We got a few bumps and bruises out there.
"We had some sloppy moments but I am not too bothered about the 24 points we conceded because we scored 68."
Widnes coach Denis Betts:
"We got caught in the headlights.
"We've had to change our team because of injuries and we are a bit beaten up at the moment.
"Leeds scored 40 points in the first half and would have been coming out for the second half thinking it was a piece of cake, so we had to go at them.
"It was one of those tough nights and we will have to respond with a couple of good home performances."
Leeds: Hardaker, Jones-Bishop, Watkins, Ablett, Hall, Sinfield, McGuire, Leuluai, Lunt, Griffin, Delaney, Ward, Bailey.
Replacements: Moore for Leuluai (21), Kirke for Griffin (21), Keinhorst for Ward (55), Clarkson for Bailey (49).
Widnes: Phelps, Isa, Marsh, Dean, Ah Van, Craven, Hanbury, Pickersgill, Haggerty, Davies, Winterstein, Allen, Cahill.
Replacements: Gerrard for Pickersgill (13), Gore for Haggerty (22), Leuluai for Davies (22), J. Kite for Cahill (29).
Sin Bin: Haggerty (60).
Ref: George Stokes (RFL).