In the men's fleet, the man of the moment Miarczynski, ranked third in the world, revelled in the strong breeze which swept across Portland Harbour on Friday, leading from start to finish in his opening race of the Championships.
Skandia Team GBR's Nick Dempsey also got off to a flying start in his home waters, with a second and a first from his two races to see him in second place overall.
"It's a good start," said the 29-year-old Dempsey.
"I just sailed really well today - I feel I'm sailing better than I've ever sailed and I feel more prepared than I I've ever been, but there's still a long way to go yet!"
Frenchman Julien Bontemps, the Beijing Olympic silver medallist, is just behind Dempsey in third place, on equal points with New Zealander Jon-Paul Tobin.
In the women's fleet, three-time European Champion Marina Alabau, who finished fourth at the Beijing Olympic Games, was delighted with her first days' performance. She held on to claim both race wins while her rivals in the fleet battled to stay on their boards in the building and gusting breeze.
"I am super happy with winning my races today," said Alabau.
"I have never won any races in more than 20 knots. Before I was very bad in more than 18 knots so I was really focussed on improving in this wind, as I knew that Weymouth would be windy."
"I'm super happy the Olympics is going to be here," the Spaniard continued. "It's flat water which is really good for me - when it is windy with big waves it is not so good for me, so I know that when it is flat water I can do well."
Italian sailor Flavia Tartaglini is in second overall, Marine Rambaud of France is third while Skandia Team GBR's Bryony Shaw currently lies in 22nd after a difficult first day. She picked up a 13th in the opening race, but was making good ground downwind in the second race when she was knocked in by a gust and dropped to 11th.
Britain's 17-year-old RS:X Youth World Champion Izzy Hamilton is on equal points with Shaw, in 23rd overall, with results of 12,12 for her opening day's efforts in this competitive senior fleet.
The RS:X World Windsurfing Championships is the second of three back-to-back World Class events being run by the RYA, supported by UK Sport, and hosted at WPNSA. The IWA Junior, Youth and Masters Windsurfing Worlds was held from 22-29 August, with the Skandia Sail for Gold Regatta - the final round of the 2009 ISAF Sailing World Cup series - set to welcome the cream of the World's Olympic Classes sailors from 14-19 September.
Click here for our RS:X World Championships page containing all the news, photos, links to live results and more from this year's RS:X Worlds.