Hangeland, who was appointed Norway captain earlier this month, prodded home the only goal of a fractious London derby which did little to dispel the doubters who believe Arsenal will fail to mount a serious bid to Manchester United and Chelsea's supremacy.
It was a measure of Fulham's early authority that it took Arsenal 12 minutes to fashion a chance of note with Emmanuel Adebayor fizzing a shot wide from 20 yards having been slid in by Robin van Persie.
Arsenal should have taken the lead seven minutes later when Theo Walcott's cross was miscued into van Persie's path by Samir Nasri, but the Dutch international fired wide of the near post with his usually reliable left foot.
And his error was punished within a minute as Arsenal's inability to deal with set-pieces reared its familiar head.
Jimmy Bullard fired over a corner from the left and Hangeland stole in unmarked to prod home his first goal in English football.
Arsene Wenger's side roared back up the other end and were unlucky not to draw level when Adebayor comprehensively beat Mark Schwarzer with a powerful header, but the outside of the post came to Fulham's rescue.
That effort aside, Arsenal were wretched, bereft of ideas, lacking in leadership and particularly the direction so regularly supplied by Cesc Fabregas, whose immanent return from a hamstring strain can't come soon enough.
The malaise lasted well into the second half, with Fabregas' Brazilian understudy Denilson out-manoeuvred by two Englishmen in Bullard and Danny Murphy.
Bobby Zamora had the chance to kill the game on the hour mark but could not divert Ki-Hyeon Seol's cross into the top corner from eight yards.
Van Persie cracked a shot wide from the edge of the penalty area with Schwarzer struggling and Nasri has a shot blocked by John Paintsil from point blank range as Arsenal belatedly cranked up the pressure.
But an equaliser failed to materialise leaving Wenger with much to ponder and one would have thought much business to conclude before the transfer window slams shut in just over a week's time.