The Rhinos opened the scoring just minutes into the game and led 22-0 at the half-time interval.
The Giants, who held second place before the game, were pushed into fourth place with 14 points, the same number as both the Rhinos and Wakefield Trinity Wildcats.
Sinfield kicked two penalties to extend the Rhinos’ advantage to 10-0, the second after Webb was taken out by Stephen Wild close to the Huddersfield line.
A third try followed quickly, Danny McGuire flying over the line and Sinfield kicking his fifth goal to make the half-time score 22-0 to the visitors.
The Rhinos kept the scoreboard ticking over after half time, Webb adding his second try from long range just moments after the restart, Sinfield converting.
Instead Leeds held out and eventually sealed their win with a late try from Matt Diskin, Sinfield adding his seventh goal to conclude proceedings.
Leeds Rhinos – 34
Ref: Richard Silverwood