The Tasmanian finished more than 10 minutes off the pace of winner Richard Carapaz during Saturday’s mountainous 234-kilometre road race from Musashinonomori Park to Fuji International Speedway.
Porte, one of three Australian riders in the race, admitted it was one of the toughest days racing he has experienced in his career but believed he should've done better.
"I'm disappointed it went the way it did," said Porte. "Riding with Luke Durbridge and Lucas Hamilton was brilliant. They did a super job for me and put me in a good position on the final climb but I just didn't have the legs."
"There was no hiding. It was seven kilometres, 10%. That's a climb straight out of the Vuelta or the Giro. With the heat and everything, it was one of the toughest days I think I've had on a bike."
The Olympic course for the Tokyo games featured 4,865 metres of elevation across five climbs and looked to suit a rider such as Porte who has excelled in similar races throughout his career.
However, it was to be for the reigning Criterium du Dauphine winner as he lost contact with the front of the race over the final climb to finish in 48th place at 10:12 behind winner and Ineos Grenadiers teammate Carapaz.
Fellow Aussies Lucas Hamilton and Luke Durbridge finished in 71st and 72nd at 16:20 behind the Colombian.
"It's always nice to represent the country but when you have days like this, it's not ideal," said Porte. "Hopefully I can recover for Wednesday's time trial."
