Machimana, 39, - a 35-fight veteran - weighed 138.60 kilograms (over 300 lbs) for the fight staged at Dr Molemela Indoor Sports Centre in Bloemfontein.
He was just fortunate that there is no limit for the heavyweight division.
He confessed after regaining his crown that he did not train. To rub salt in the wound, the belt would not fit around his waist.
"I was told the fight will be on October 26 but I then got told only last week that the fight will now take place on Friday because SABC Sport had given the promoter [Lebo Mahoko] tonight's [Friday's] date," said Machimana who won the fight by scores of 117-111, 116-112 and 115-113.
"I thought it will be over in four rounds but Justice was there until the last [round] and I will speak to the promoter about giving him a rematch because he deserves it," Machimana said.
He improved his record to 23 wins in addition to 10 knockouts and two losses.
Siliga, who fought his first 12-rounder on Friday, looked superbly fit at 102.45kg.
"He promised to knock me out in five rounds but here I am after 12 rounds. He was a better man tonight but I will come back and work harder. I would really love to fight him again," said the 30-year-old. Siliga suffered his sixth loss against six wins, all by knockouts.
The heavyweight fight topped the five-bout card of Dream Team Promotions.
