Olympic champion Humphries appeared on course for her seventh win from eight this season after leading by 0.08seconds following the first run however German Kiriasis had other ideas.
Having claimed four top-three finishes this season but not a win, the 38-year-old produced a storming second run in Austria to beat Humphries by just one hundredth of a second.
With the Igls World Cup round also acting as the European Championships, Kiriasis upgraded the silver she won last year to gold while also putting a halt to Humphries' Triple Trophy bid.
Awarded those who win the final three rounds of the season, Humphries no longer qualifies while her lead in the overall World Cup standings has been reduced from 202 points to 187.
However with 225 points available for a win, Humphries is still likely to be the first Canadian woman to be crowned World Cup champion at the season finale in Sochi, which will also act as the Olympic test event.
Humphries, pushed by Chelsea Valois, clocked 54.20seconds to lead Kiriasis, pushed by Franziska Bertels, by 0.08 after run one with Anja Schneiderheinze and Jazmine Fenlator a close third and fourth respectively.
However the top order dramatically changed following run two with Kirasis posting 54.37 to Humphries' 54.46 to leapfrog the Canadian Olympic champion and win by 0.01.
Fenlator overtook Schneiderheinze for third, just 0.04 further adrift, however fourth was enough for the German to take European silver as part of a one-two-three for the nation.
American Elana Meyers was fifth before Cathleen Martini in sixth and ultimately third on the defence of her European title with Brit Paula Walker seventh overall for fourth in the continental standings.
That matched her performance of the last round in Koenigssee but sees her drop from eighth to ninth in the World Cup standings while compatriots Victoria Olaoye and Kelly Denyer were 16th overall.
- Sports & Recreation