In a flattering scoreline, the Danish champions enjoyed two extended spells of pressure before three goals in the final 11 minutes calmed Roberto Di Matteo's nerves
Juan Mata opening the scoring in the first half, but two extended periods of pressure from the Danish champions could, and perhaps should, have led to a different game.
But, David Luiz’s thunderous free kick, Mata’s second and a Ramires tap-in wrapped up Chelsea’s first win of their cup defence.
Roberto Di Matteo made just three changes to his side which beat Arsenal on Saturday, indicating how seriously the Italian was taking the threat of the Danish champions, as John Terry, John Obi Mikel and Eden Hazard were replaced by Gary Cahill, Frank Lampard and Victor Moses.
Nordsjaelland named an unchanged side to the one that lost 2-0 to Shakhtar Donetsk in matchday one.
Chelsea nearly got off to the perfect start when Oscar stood the ball up beautifully inside the area for Moses to simply convert into an empty net from two yards, only for highly-rated Nordsjaelland defender Jores Okore to do enough to head the ball against the post.
It was one-way traffic, with the holders dominating proceedings, with an opening goal seemingly inevitable as Oscar and then Lampard both went close within the first 10 minutes, without being able to test Jesper Hansen.
Nordsjaelland finally ventured out of their own half soon after, with Joshua John hitting a wild effort from distance.
But, the hosts took heart from that brief showing and slowly grew in to the game. John again led the charge forward but instead of unleashing a rash attempt at goal, the striker looked up and found Kasper Lorentzen inside the area, but the former Brondby man's effort was blocked by a last-ditch lunge from Ashley Cole.
Lorentzen, though, were made to rue that miss shortly afterwards when Enoch Adu was caught in possession by Fernando Torres, who found Lampard in space centrally. The influential midfielder then fed Mata, who was charging down the right channel, to slot home and give the English side the lead.
Nordsjaelland appeared demotivated by going behind, losing their previous impetus, with Chelsea seemingly content to sit on their narrow lead until the half-time break.
The Blues had the ball in the back of the net within a minute of the restart after Torres had blocked an attempted clearance by Patrick Mtiliga and found Oscar in space 15 yards out, but the Brazilian was correctly flagged offside.
The home side were regimented throughout, if not a tad naive, as they persisted on passing the ball out of defence, despite continually finding themselves under pressure in their own half.
They, again, gradually grew in confidence though, and, again, perhaps should have scored when Okore, who was strong and reliable for the duration, floated an inch-perfect cross onto the head of Mikkel Beckmann inside the box, but the forward’s header looped over the bar.
And, just minutes later, Nordsjaelland again found themselves in a promising position when Beckmann hit a first-time effort across his body with Petr Cech motionless, only to see the ball sliced away from the target.
The hosts were getting closer, and only a glorious Cech save denied Nordsjaelland in their best chance of the game when John cut inside from the left, skipping past David Luiz, and cracking a fierce shot towards the far top corner, which the goalkeeper managed to tip onto the post.
However, as in the first half, just when the home side were at their most threatening, Chelsea pounced.
First, Luiz hit a stunning free kick from the left-hand corner of the area that flew in via the near post, before Mata - Chelsea’s best player on the night - first tried to find an onrushing Lampard inside the box but, with the pass blocked, tried his own luck and coolly slotted the ball under Hansen.
Ramires gave the scoreline a unjust look in stoppage time, rolling in a fourth after neat play from Torres and Oscar, with Di Matteo visibly relieved on the touchline after an extended period of pressure from the Superliga champions.