In a match held over from late Friday when the two men parted company at one set all, Djokovic once again showed the composure and killer instinct that have been a feature of his stunning unbeaten run since January.
He will next play back-to-form Frenchman Richard Gasquet for a place in the quarter-finals in a tie that is sure to fire up the partisan Paris crowd on Sunday.
The match resumed out on the Suzanne Lenglen showcourt 18 hours after fading light had forced them off and Djokovic was the first to be put under pressure saving a break point in the fifth game after a 23-shot rally.
But in the following game he broke Del Potro to take a 4-2 lead and from there he comfortably pocketed the second set.
The tempo and ball-striking continued to be fierce into the fourth set and once again it was Djokovic who struck first setting up two break points in the third game with a deft drop shot after a punishing 26-stroke rally.
Del Potro saved the first of these but an untimely double fault followed and Djokovic had the break.
The second seed got to 4-1 and serving, but let his concentration slip for once to allow Del Potro to get to 0-30.
The giant Argentinian then defied his size by sprinting in to return a near perfect Djokovic drop shot and when the Serb blasted long, the South American had a lifeline.
It did not last long.
Djokovic once again unleashed a salvo of big hits off both flanks and Del Potro was unable to stay the pace, fluffing a weak backhand into the net on set point.
The Serb comfortably served out for his 40th consecutive win in 2011.
Djokovic will match John McEnroe's 42-match winning streak set from the start of 1984 should he reach the semi-finals here.
He is also aiming to become the first player since Jim Courier in 1992 to win the Australian and French Open titles in the same year, taking him halfway to the fabled Grand Slam of tennis.
- AFPTags: sport, tennis, france