Top-ranked Giles Scott of Britain powered to second- and first-place finishes in high waves and 20-knot winds on the Niteroi ocean course.
That moved Scott, his nation's best medal hope since four-time Olympic champion Ben Ainslie's retirement, into first place with five preliminary races to go after Tuesday's disappointments on fluky Guanabara Bay.
World No. 35 Vasilij Zbogar of Slovenia is five points back and in second place overall.
"It couldn't have been more different today," Scott told reporters. "We went from racing underneath a mountain in very light and fickle winds to be out in strong winds and big seas. (It) made for really full on racing."
Second-ranked Frenchman Jonathan Lobert moved up into fifth place from 12th after racking up a 26-second win over Scott in the first race of the day and a seventh in the second.
In the men's Laser class, No. 2-ranked Tonci Stipanovic extended his overall lead on 26 points while continuing Croatia's hunt for its first Olympic sailing medal.
Sailing in strong winds off Copacabana Beach, Stipanovic finished ahead of Britain's Nick Thompson and Rutger van Schaardenberg of the Netherlands.
Twice Olympic gold medallist and nine-time Laser world champion Robert Scheidt, 43, improved his chances for a record sixth medal in six games as Brazil's "El Demolidor" moved into fourth from eighth.
In the women's Laser Radial class, defending gold medallist Xu Lijia of China surrendered her lead to Ireland's Annalise Murphy, whose 19 points put her one ahead of Denmark's Anne-Marie Rindom and two ahead of Netherland's Marit Bouwmeester.
Wednesday also showcased the first day of racing in the 470 two-person dinghy and Nacra 17 mixed-sex catamaran, both classes contending with light winds on Guanabara Bay.
Helmsman Sime Fantela and crew Igor Marenic of Croatia moved into top spot after a 55-second trouncing of New Zealand's Paul Snow-Hanson and Daniel Willcox, who sat in third after two races. Australia's Mathew Belcher and Will Ryan are in second.
Japan's Ai Kondo Yoshida and Miho Yoshioka lead the women's 470, with Slovenia's Tina Mrak and Veronika Macarol in second after a protest disqualified New Zealand's Jo Aleh and Polly Powrie from the first of two races.
Aleh and Powrie, the defending gold medallists, failed to take a penalty turn after interfering with Austria's right-of-way.
Sweden's Matias Buhler and Nathalie Brugger lead the Nacra 17, followed by Ben Saxon and Nicola Groves.
(Editing by Mark Lamport-Stokes)
