The 28-year-old Italian scooped gold ahead of Finland's Kaisa Makarainen by just 0.6 seconds as both missed the target on just one occasion on the Austrian circuit.
Aggressive skiing proved key for the Olympic two-time bronze medallist to cross the 7.5km women's sprint finish line in 21:04.9 and deny Makarainen a third title of the campaign.
Highlights: Men's rely at Hochfilzen
Russia's Ekaterina Yurlova-Percht finished third after shooting cleanly throughout but could only finish 24.4 seconds behind the leader.
The victory ensures Wierer retains the yellow bib as the leader of the season-long overall rankings heading into the 10km pursuit in Hochfilzen on Saturday.
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