Unbeaten after the first eleven of the fourteen scheduled clashes, Carlsen can no longer be joined by his opponent.
He thus won for the fifth time the title of world champion which he has held continuously since 2013.
The world number 1 in the points classification, favorite of the match, put an end to the ordeal of Nepomniachtchi, who resigned himself to a new abandonment on the 49th move and 3:20 of the game on Friday.
After five draws to start, the Norwegian broke the deadlock by winning the longest game ever in a world chess championship, after 136 moves and nearly 8 hours of fighting.
He then ruthlessly took advantage of the gifts given by his challenger who blundered three times in the following rounds.
The 31-year-old Norwegian is making more of his sport's history and is now just one length behind the record for world championship victories held by Germany's Emanuel Lasker, dating back to the start of the 20th century.
Russians Garry Kasparov and Anatoly Karpov also have six world championship wins, but some came when two circuits co-existed, which Magnus Carlsen never did.
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