Inside centre McMullen strode over the line virtually unopposed in the 45th minute for a try, fly-half Ross kicked 16 points while scrum-half Dickens skippered the side.
Last month Alan Gaffney's men totally outclassed the Yorkshiremen 31-7 in the Guinness Premiership and the gulf in quality was again graphically illustrated at times.
Saracens outscored Leeds by six tries to four but, in truth, staving off the threat of relegation is all that matters this season at Headingley for Stuart Lancaster and his players.
And there were plenty of positive signs from which Lancaster could draw encouragement as centre Andy Tuilagi enjoyed an impressive first start of the season and Fijian international Appo Satala made a try-scoring debut on the wing.
The Yorkshiremen largely matched Sarries in the first half and only trailed by five points at the break.
Leeds fly-half Alberto Di Bernardo kicked his side ahead with a third-minute penalty which was soon cancelled out by a three-pointer from Ross, and in the 18th minute Saracens centre Rod Penney scuttled under the posts for the first of his tries.
Ross converted but Leeds produced their best move of the game shortly before the half hour mark when a bewildering array of inter-passing culminated in Erik Lund crossing in the left corner.
Di Bernardo failed to convert from near the touchline and another Ross penalty edged Sarries 13-8 ahead at the break.
In the second half the visitors produced a masterclass in clinical finishing to run in five tries to seal the game.
After Di Bernardo struck a 43rd-minute penalty, McMullen scampered over the line and Penney claimed his second soon after.
Although prop Mike McDonald barged his way over for Leeds in the 57th minute, two tries in four minutes from Edd Thrower and replacement Moses Raulini further exposed Leeds' defensive flaws.
The spirited hosts hit back through an exhilarating effort from debutant Satala, but Saracens hit back with a late, sixth try from Kevin Sorrell which Ross converted from under the posts.