Just 24 hours later, teammate Saori Yoshida could become the second Japanese woman to pull that off.
Japan has ruled women's freestyle wrestling since it was added to the Olympic program for the Athens Games in 2004. That doesn't look likely to change during the London Games.
Icho won golds at 63 kilograms in Athens and Beijing. Yoshida has taken both at 55 kilograms — and both are favourites to repeat as Olympic champions in London this week.
The women's 48 and 63-kilogram tournaments are on Wednesday, and Japan is favoured to sweep them behind Icho and Hitomi Obara.
Yoshida will go for her third straight Olympic title when the 55 and 72-kilograms are held on Thursday.
Icho has dropped just three periods in her 61 matches since returning from an 18-month hiatus following her win in Beijing.
Two of the three periods Icho dropped since her return came at the hands of American Elena Pirozhkova. She said last month that she feels like she's got a legitimate shot at defeating Icho after training with her in Colorado Springs, Colorado.
But it will take a massive upset to unseat Icho — and she might not be the only woman from Japan to win Olympic gold on Wednesday, either.
Obara won six world titles at 51 kilograms, a weight not included in the Olympics, before retiring four years ago. She returned in 2010 at 48 kilograms and has won the last two world titles.
Obara's path to a gold may be tougher than Icho's. Ukrainian Irina Merleni won gold at 48 kilograms in Athens in 2004 and bronze in Beijing, and Canada's Carol Huynh is the defending Olympic champion.