Dujardin and Britain's two other team riders have an average score of 79.407 per cent. Germany, which has dominated the sport for much of the past 50 years, is a close second at 78.845 per cent.
The Netherlands is in third place with 76.809 per cent, followed by Denmark in fourth and the United States fifth.
The riders will return to ride the Grand Prix Special on Tuesday to complete the team event. The 18 highest-placed competitors from the team competition will perform a freestyle ride on Thursday for individual medals.
Germany's Kristina Sprehe on Desperados broke the former Olympic record for a Grand Prix test by nearly a full percentage point earlier in the day with a 79.119, but Dujardin improved on that with her 83.663 to take first in the individual standings and also to put Britain into the team lead.
"I was hoping for an 80 or 81 before today," Dujardin said. "To come to the Olympics and smash that is crazy."
Also breaking the former Olympic mark were Adelinde Cornelissen of the Netherlands on Parzival with 81.687 for individual second, and Helen Langehanenberg of Germany on Damon Hill with 81.140 for third.
"Parzival was distracted by the crowd at the start," Cornelissen said. "I know we can do over 80 per cent and we needed a good score for the team."
U.S. rider Steffen Peters, a four-time Olympian and a former World Cup champion on Ravel, scored 77.705, finishing in sixth individually. Tina Konyot scored 70.456 per cent for the U.S. on Calecto V and stands 27th.
"I think it's my best Olympic Games ride," Peters said. "I hope we can step it up in the Grand Prix Special, which is Ravel's best test."
Rafalca, co-owned by the wife of U.S. presidential hopeful Mitt Romney and ridden by Jan Ebeling, scored 70.243 per cent to place 30th out of 50 riders. Ann Romney, Mitt Romney's wife, was in the stands Thursday to watch the first day of the competition.Suggest a correction