Adrian denied James Magnussen in his bid to add the Olympic crown to the world title when he out-touched the Australian by one one hundredths of a second.
Magnussen, known as 'The Missile', had to settle for silver as Adrian clocked a winning time of 47.52.
Brent Hayden of Canada was third in 47.80, with world record-holder Cesar Cielo back in sixth.
Gyurta broke the world record as he edged out Britain's Michael Jamieson in a final length head-to-head in 2:07.28, clipping 0.31 off Christian Sprenger's 2009 mark.
Jamieson, fifth at last year's World Championships, touched in 2:07.43.
Gyurta, who won silver in Athens aged 15, said: 'It was hard for me, but I managed to do it.
'I can't believe it, it was my dream when I was young (to get the medal and the world record).'
'(Which one means the most) I really can't say, I am just so happy.'
Meanwhile, the USA set an Olympic record of 7:42.92 in the women's 4 x 200m Freestyle Relay, and China's Jiao Liuyang added the 200m Butterfly title to the World Championships gold she won last year.
Rebecca Soni set the second world record of the night when she lowered Annamay Pierse's mark in the 200m Breaststroke semis to 2:20.00.