Junior returned a fifth and then a win in race three and with 34 points was in sixth overall at the end of the first day.
Visilij Zbogar from Slovenia was in first with 11 points while Croatian Ivan Kljakovic-Gaspic was in second place seven points ahead of Murdoch.
Meanwhile, Gemma Jones and Jason Saunders also opened strongly at the Nacra 17 World Championship at The Hague, Netherlands, which got under way yesterday although trying conditions meant that just one of two (split) fleets completed their races.
The Nacra 17 is the new Olympic multihull class and is sailed by one female and one male.
Kiwi contenders Jones and Saunders have made an encouraging start with a seventh and a third on the water to hold second place.
"It was tricky sailing, the conditions were difficult," Saunders said. "It was not easy to start with that current and we couldn't always keep the lay line. We are not used to this. I sailed this water also in 2010 when I attended the 470 worlds, so I know it a little. The second race was even more difficult, because the wind started to die out at the end.
"But we were happy to sail two races and not to have been waiting all day again. It's been two long days waiting at the beach. For the next two days we hope to sail as many races as possible."
Despite spending hours on the water those in the yellow fleet including Kiwi crews Nicole van der Velden and Tomer Simhony and Gareth Moore and Vickery Francis were yet to record any race results.
Racing resumes at both regattas today with medals to be decided on Sunday. APNZ