Defender hopes to be King's replacement at the heart of defence
The Three Lions had raced away to an early lead courtesy of an excellent pass from Emile Heskey that skipper Steven Gerrard buried in the back of the net. But Green threw away the lead by showcasing the latest clanger by an English goalkeeper, fumbling a tame shot by Clint Dempsey that rolled over the goal-line.
The goal proved to be one that saw Fabio Capello's men drop two points in the Group C opener, with games against Algeria and Slovenia yet to come.
The 30-year-old custodian has been the subject of heavy criticism following the goalkeeping gaffe against the Americans, but his West Ham team-mate insists that the former Norwich City player is wiser for the experience.
"Robert Green is 100 per cent ready to play on Friday," Upson said on his club's official website.
"These mistakes happen, although I cannot ever recall him doing anything like that [before].
"He is a big boy and has handled it really well. He just has to put it behind him and move on."
Meanwhile, Upson is himself competing among his peers for a chance to start against Algeria, following the recent groin injury sustained by centre-half Ledley King.
The former Birmingham City and Arsenal defender insists that he is itching to get out on the pitch and play a part in the proceedings.
"The nature of the industry we are in means you are always going to suffer personal setbacks," said Upson.
"I am desperate to play my part. I have to be patient, keep focused and keep working hard in training.
"That has been my focus since I have been here. That is not going to change for the duration of the tournament. Everything else is outside my control."