Ben Ainslie warned his rivals they had "made him angry" as he reignited his quest for a fourth Olympic gold medal.
The Briton hit back with a first and a third to close on Finn class leader Jonas Hogh-Christensen to three points with two races and the medal race left.
Ainslie claimed Hogh-Christensen and Dutchman Pieter-Jan Postma teamed up against him, forcing him to do a penalty turn in race two.
"They've made a big mistake," said three-time Olympic champion Ainslie.
"They've made me angry and you don't want to make me angry."
The 35-year-old resumed after the rest day with his pursuit of a fourth Olympic title in the balance.
Ainslie had not managed to beat surprise leader Hogh-Christensen in any of the first six races and was 10 points behind the Dane.
But he made an aggressive statement of intent in the first race in big waves and strong winds out in Weymouth Bay.
Ainslie led off the start line leaving Hogh-Christensen in his wake, but the Dane fought back from eighth to fourth on the first downwind leg before capsizing and losing 30 seconds as he righted his boat.
Postma overhauled Ainslie briefly but the Briton regained the lead to cross the finish line with a substantial gap and pumped his fists in delight.
Hogh-Christensen came home in eighth to see his overall lead narrow to four points.
"I had a day off yesterday and I watched the girls winning the gold medal in the rowing and Bradley Wiggins smashing the time trial and that was a big inspiration," said Ainslie. "I thought to myself, 'If they can go out and do that, why can't I?'
"You see British people performing really well at the highest level and it inspires you to do the same."
In race two, the action heated up even more as the Dane and the Dutchman both claimed Ainslie hit a mark. Ainslie says he did not, but took a penalty turn as a precaution, fearing he would lose in the protest room later with two voices against one.
But that fired him up and he made up 70m on the final downwind leg to overtake Hogh-Christensen for third. After crossing the line, Ainslie was seen to gesture angrily towards the Dane.
"The Dutch and the Danish guys teamed up against me to claim I hit the mark when I didn't," said Ainslie. "I was seriously unhappy about that. It's disappointing. It's happened to me a lot in the Olympics before but I guess I'm older and wise enough to know not to fall for it.
"But those guys better watch out. I can tell you, it's made me pretty angry to make amends. It is sport, they're going to take any advantage they can. I don't particularly appreciate it because I'm sure I didn't hit the mark. Maybe their time will come."
Ainslie was the subject of a protest from a French sailor in the second race in Athens and opted not to take a penalty turn at the time.
He lost his argument in the protest room later and was disqualified from the race, giving him a 26th place. That result instantly became the one score he would discard and left him with no room for error for the rest of the regatta, and he was forced to fight extra hard to secure his third gold.
Hogh-Christensen was unrepentant and claims he saw Ainslie hit the mark. "Ganging up is a hard allegation," he said. "I don't think anybody teams up to call somebody on that.
"I saw him hit the mark, I think the Dutch guy saw him hit the mark, so if two guys see it, it's probably because he hit the mark. There was no bad words from either of us, we just called him on it.
"He decided to do what he had to do and he took his penalty. If he was so sure he didn't hit the mark, why do you take the penalty?
"The exchange of words was probably unnecessary but that's the way life is. What Ben said is between me and Mr Ainslie."