Tretiakov leads by 0.09 seconds at the halfway stage as the Latvian faces an uphill battle to keep hold of his World Championship title.
Dukurs has a 223-point lead going into the ninth and final World Cup round in Sochi later this month having won seven of eight races this season, however he trails Tretiakov at the worlds.
Tretiakov, who was the last man to win the World Cup title that wasn't Dukurs in 2009, clocked 1:07.85 minutes first time out and 1:07.92 with his second run with two-time defending champion Dukurs managing just shy of both with 1:07.87 and then 1:07.99.
Tretiakov and Dukurs were the only two sliders to duck under the 1:08.00 barrier with another Russian, Sergei Chudinov, lying in third place after two runs, 0.65 behind his compatriot.
Tomass Dukurs is then another 0.61 back in fourth, a place Brit Kristan Bromley, who earlier in the day saw partner Shelley Rudman win the women's title, had occupied after run one.
Bromley, the world champion in 2008, clocked 1:08.58 first time out for fourth but dropped to eighth with 1:08.91 second time out with Frank Rommel fifth, John Daly sixth and Jon Montgomery seventh.
Fellow Brit Dominic Parsons is 12th overall, 2.32 behind Tretiakov, while compatriot Ed Smith is just three places and 0.22 further adrift in 15th at the halfway stage in St Moritz.
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