Like the thousands of spectators in attendance at Suncorp Stadium, Horn admitted that he expected a tougher fight from arguably Australia's most famous boxer.
After leaving fans waiting an hour past the scheduled start of the fight, Horn wasted no time once the bell rang.
The 30-year-old, aiming to bounce back from his first professional loss to Terence Crawford in June, delivered a left-hook which floored the ex-rugby league player midway through the first round on Friday night.
Horn came out fast and landed a right hand early and set about putting the 43-year-old under pressure.
Following the fight the 43-year-old Mundine confirmed that it would be his last career fight.
Mundine fell and the fight was over, a win in 96 seconds by knockout.
Confident in his performance at the 71kg catchweight, Horn said he now had to work out if his future lies at welterweight or explore options in heavier divisions.
"I feel really, really strong at this weight", Horn said immediately after the bout.
"I guess we've got to sit down and talk about that still".
"I was ready I prepared well but it's just boxing man you get caught sometimes".
"It couldn't have went to a better guy". No excuse I had a tremendous camp.
México, EE.UU. y Canadá firman el T-MEC
El acuerdo comercial , que sustituirá al Tratado de Libre Comercio de América del Norte ( TLCAN ) vigente desde 1994, aún debe ser ratificado por los congresos de los tres países para su posterior entrada en vigor.