In Thursday evening's second free practice session, which is held in similar conditions to qualifying and the race, Lewis Hamilton led a Mercedes 1-2 ahead of Russell, with Aston Martin's Fernando Alonso in third.
Overwhelming favourite Max Verstappen was sixth as Red Bull put more emphasis on long runs.
And while Russell admitted Mercedes' progress compared to testing "exceeded expectations", he thinks Red Bull is still a cut above on race pace.
"We're not getting carried away with ourselves. The qualifying pace looked really strong, we still need to understand why it was so good," Russell said.
"We made some changes from the test and it exceeded expectations. But ultimately, the long run pace is where it all happens and Max is still ahead of us.
"It was very close with Fernando, Lando [Norris] and the Ferraris, Lewis and I were very similar as well, so we have a real fight on our hands.
"In race pace we were very pleased with the day, the car is performing really well but we're not going to get carried away with the timesheets just yet."
Mercedes' one-lap pace does provide it with a glimmer of hope that Red Bull isn't "out in the distance", as Hamilton phrased it last week.
Source: Autosport