The 31-year-old was never threatened, leading the 3,000m event from start to finish as she claimed the first gold medal of the championships, nearly eight seconds ahead of Wojtyra.
In the women’s team sprint final, reigning champions Jinjie Gong and Tianshi Zhong of China were disqualified having finished ahead of Russia.
Anastasia Voinova and Daria Shmeleva were handed the title after judges ruled one of China’s changes illegal.
Australia’s 11-times world champion Anna Meares failed to add to her medal collection as she and Stephanie Morton were edged out for the bronze medal by German duo Miriam Welte and Kristina Vogel.
It was still a satisfactory opening day though for Australia with Wiasak’s gold, albeit in an event that will not feature on the Olympic schedule in Rio later this year.
“Being the defending champion there was extra pressure. Every world title is special and I’m so pleased that I could win for a second time in a row,” Wiasak, hoping to get a place in the team sprint in Rio, said.
New Zealand beat the Netherlands in a closely-fought men’s team sprint final while Spain’s Mora Vedri powered away from the leading bunch late in the 15km scratch race, 60 laps of the track, to take the gold medal ahead Ignacio Prado of Mexico and Switzerland’s Claudio Imhof.
All eyes on Thursday will be on Briton Bradley Wiggins as the former Tour de France winner contests the men’s team pursuit after the hosts’ quartet set the fastest qualifying time on Wednesday to reach the semi-finals.
Wiggins, 35, has returned to the track in the hope of making the plane to Rio where he would be chasing an eighth Olympic medal, 16 years after taking a team pursuit bronze in Sydney.
“Bradley has proved he belongs in that team. He was incredible,” Britain’s endurance coach Heiko Salzwedel said.
“There’s definitely more in the tank than we have seen here today.”
(Reporting by Martyn Herman, editing by Ed Osmond/Toby Davis)