“The winner of a game of chess is he who makes the last mistake but one.” - Probably Lasker but people often attribute this quote to Tartekower[1]

Ding won the WCC due to a terrible blunder by Nepomniachi. Good as he was Fischer blundered his bishop like a patzer during his WCC match against Spassky and came back to win the match. Chess games between humans are generally decided by somebody making a mistake. Is that luck?

Of course not. To put himself in a position to benefit from that luck he had to play extremely well for the entire match so that it would be even going into the last game.

[1] https://chesshistory.com/winter/extra/mistake.html