Adrian Pertl leads the slalom after the first run, with the second run in progress. The 24-year-old clocked 52.24 seconds, 0.14 faster than Italian youngster Alex Vinatzer.
Norwegian Sebastian Foss-Solevag was third quickest, 0.16 back, with Sweden's Kristoffer Jakobsen fourth, 0.18 down.
Frenchman Clement Noel was fifth at 0.34 while his team mate and race favourite Alexis Pinturault, who crashed in Friday's giant slalom with victory in sight, could manage seventh place in the soft snow conditions, nearly half a second off the pace.
‘Can you believe that?’ - Pertl leads slalom at halfway stage on debut
Norway are well-placed for a medal with Henrik Kristoffersen, winner of 19 World Cup slalom races, sitting in sixth spot ahead of leg two.
Several skiers failed to complete their first runs including former world slalom champion Jean-Baptiste Grange.
Only the top 15, rather than the top 30, will go in reverse order in the second leg as the temperatures at the Italian resort are expected to create slushy snow.
The men's slalom concludes the racing at this year's championships which have taken place without fans because of the Covid-19 restrictions.
The Alpine skiing world championships are live on Eurosport. Watch it on eurosport.co.uk and the Eurosport app.