KHL Eastern Conference leader Sibir Novosibirsk suffered a surprise 5-3 home defeat at the hands of Metallurg Novokuznetsk on Thursday.
A six-goal second period left Sibir 5-1 down, before the hosts rallied in the third to salvage some pride.
Sibir stays top of the conference standings, but has played three more games than second-placed Traktor Chelyabinsk, two points adrift.
Alexei Yefimov opened the scoring for Metallurg in the first minute of the second period, slotting the puck past Sibir goaltender Jeff Glass off Alexander Mereskin's assist from behind the goal.
A loose-puck leveler from Sibir's Mikhail Fisenko brought little respite before Metallurg's goals rained in, Zakhar Arzamaztsev scoring from out wide before Alexander Bumagin hit the target twice and Mereskin got his name on the scoresheet too.
Jonas Enlund and Artyom Voroshilo scored for Sibir in the third period, but the hosts did not come close to taking the match to overtime.