Hamilton's surge came as the field switched onto the yellow-marked soft tyre: first he did 1m 39.817s, then cut that to 1m 39.630s. Team mate Nico Rosberg, who had earlier been fastest on the hard tyre with 1m 41.508s to Hamilton's 1m 41.750s, made a mistake and ran wide on the best of his own flying laps and was left in fourth place with 1m 40.542s after his soft-tyre runs.
Between them, McLaren continued their strong start in Russia as Kevin Magnussen jumped to second on 1m 40.494s, albeit 0.864s down on Hamilton. And Fernando Alonso made a big improvement in the final half hour to go third for Ferrari after several laps on the soft tyre, with 1m 40.504s.
In general the times have been very tight thus far, Hamilton excepted. Williams' Valtteri Bottas recovered from a tyre blanket malfunction this morning to slot into fifth on 1m 40.573s - three hundredths of a second down on Rosberg, and fractions ahead of Jenson Button, who set 1m 40.718s in the second McLaren, and Felipe Massa on 1m 40.731s in the other FW36.
Daniil Kvyat described his Toro Rosso as "lazy" but remained the fastest Renault-engined runner in eighth, on 1m 41.108s.
Red Bull's soon-to-be deperating four-time world champion Sebastian Vettel was ninth on 1m 41.396s, while team mate Daniel Ricciardo never got out of the midfield and then suffered an early exit when his RB10 rolled to a halt in Turn 11 with eight minutes of the session remaining, briefly bringing out the red flags. The Australian ended the session 13th, on 1m 42.061s.
Jean-Eric Vergne was 10th on 1m 41.531s in the second Toro Rosso, ahead of Kimi Raikkonen on 1m 41.630s in the other Ferrari, and Nico Hulkenberg in the lead Force India on 1m 41.677s. The latter's team mate Sergio Perez was 14th with 1m 42.090s, ahead of Adrian Sutil's Sauber on 1m 42.233s, the Lotuses of Romain Grosjean and Pastor Maldonado on 1m 42.892s and 1m 42.905s, and Esteban Gutierrez's Sauber on 1m 43.055s.
Caterham duo Marcus Ericsson and Kamui Koabyashi were 19th and 21st respectively - on 1m 44.135s to 1m 44.952s - sandwiching the sole Marussia of Max Chilton, who lapped the circuit in 1m 44.530s.
The circuit continued to ramp up in pace as the session wore on, so the times can be expected to tumble even further on Saturday if the weather remains fine and dry.