The fastest goal scored from the start of a period is 4 seconds, by Denis Savard in 1986. The fastest goal scored at the start of a game is 5 seconds, by Doug Smail in 1981, Bryan Trottier in 1984, and Alex Mogilny in 1991.
WAS IT NOT THE CHELSEA PLAYER IN THE FA CUP FINAL No - own-goal! Scored in 1977 for Cambridge United after six seconds. Punt up-field from the kick-off, off defender's head, and in. I suspect it's actually faster than the fastest goal in league history.
The fastest goal ever scored in a World Cup match was scored by Turkey's Hakan Sükür after only 11 seconds against South Korea in 2002. Prior to that it was England's Bryan Robson who scored against France in the Spain 1982 World Cup after 27 seconds.