Fox-Pitt scored 37.0 penalties after the opening day in Rio to lead the dressage.
Astonishingly, Fox-Pitt only returned to action in April following a nasty fall in a cross-country event last October which left him with a head trauma.
Rio 2016
Eventing star Phillip Dutton delighted with his first Olympic medal in American colours
10/08/2016 AT 13:44
"I've had an interesting last few months," he said.
I've been very lucky - I'm lucky to be here. It was very special riding into the arena today.
"This is my fifth Olympics - they've all been useless! It would be great if this one went well."
Day two of the dressage follows on Sunday with the cross-country on Monday.
Both the team and individual medals will be decided with the show jumping on Tuesday.
Britain currently lie third in the team competition with Germany and Australia leading the way.
Rio 2016
France wins equestrian team eventing gold while Jung takes individual for Germany
09/08/2016 AT 16:07