Scrum-half Jonny Lomax led the way with a 22-point haul from two tries and seven goals from eight attempts while wingers Ade Gardner and Gary Wheeler both scored a brace of touchdowns.
Leeds trailed 30-0 early in the second half and, although they averted a whitewash, they could not avoid humiliation at the hands of last October's beaten Grand Final opponents.
The City Reds had conceded 96 points in their previous two games against Leeds and Catalans but showed no lack of confidence as they put the Bulls to the sword in a torrid first half. They scored six tries before the interval to go in leading 30-6.
Lloyd White notched two tries for Widnes who were level 30-30 until Cameron Phelps' vital try six minutes from time.
Michael Dobson inspired Rovers' success with five assists and six goals as a run of 24 unanswered points underlined their dominance after falling 18-6 behind. The Giants had taken a grip on the game with converted tries to Luke George, Scott Grix and Greg Eden in the opening 18 minutes.
Liam Watts had replied for Rovers before they reeled off four unanswered tries either side of half-time. Dave Hodgson got the ball rolling on 35 minutes before Kris Welham, Josh Hodgson and Scott Taylor crashed over in a match-winning burst.
Peter Gentle's side completed the high-profile signing of England forward Gareth Ellis on Wednesday and had too much for a Tigers side that have yet to win since their victory at Salford in round one. The lead exchanged hands on several occasions in a frantic first half, but Hull took control after the interval and eventually ran out comfortable winners.
Danny Tickle scored one of his side's seven tries and finished with 18 points following a flawless kicking display, while Rangi Chase laid on four scores in a losing cause for Castleford. The Tigers were able to welcome back influential duo Danny Orr and Josh Griffin, who each missed last weekend's defeat to Huddersfield Giants through injury.
Winger Peter Fox scored his first tries since the Wildcats' opening-day win at Widnes and the home side led 30-6 after 51 minutes before withstanding a late rally from their French visitors.
Scott Dureau, Vincent Duport and Clint Greenshields all scored late tries as the Dragons cut the gap to just eight points, but Wakefield stand-off Isaac John closed out the game with a penalty on the final hooter.