Australia's reigning Olympic champion Tom Burton took over the lead from New Zealand's Sam Meech as championship racing began at the International Laser Class Association Laser Standard Men's World Championship in Sakaiminato.
From today sailors have been divided into gold, silver and bronze fleets, with 52 boats in each, following three days of qualification.
All of the qualifying scores still count towards the overall total with Rio 2016 gold medallist Burton finishing eighth and then second across the two races to top the pile.
He now sits on 27 points with a 21st-place finish currently discarded.
Meech, who won both races held yesterday in Japan's Miho Bay, has slipped back to second on a score of 33.
The Rio 2016 bronze medallist was 17th in the first race, which is currently discarded, and then 12th.
Germany's Philipp Buhl sits third on a total of 40 with fewer than 20 points separating the top six.
This includes sixth-placed Sergei Komissarov of Russia who has 45 points after winning today's first race.
He endured contrasting fortunes, however, after ending the second trip to the water in 46th position which is currently discarded.
Ireland's Finn Lynch won the second race after ending 42nd first up and is 33rd overall.
Robert Scheidt, Brazil's double Olympic gold medallist, sits 13th on 58 points.
In addition to the quest to become world champion, five sailors will qualify their country for an entry in the men's one-person dinghy event at next year's Olympic Games in Tokyo.
The penultimate day of racing is tomorrow.