Climbing specialist Polanc, who races for the United Arab Emirates (UAE) team, was part of a four-man breakaway that pulled free early in the 181 km ride from Cefalu.
Despite being left on his own for the last 16 km of the 18.1 km climb to the summit, Polanc held on to solo over the finish line in just over 4hr 55min.
"It was probably the hardest day of my life," said Polanc. And most of the peloton agreed.
While locals are used to seeing sparks from the regular eruptions on Europe's highest active volcano, a tough headwind ended hopes of a stage four duel between defending champion Vincenzo Nibali and Colombian challenger Nairo Quintana.
