The British driver ended the more representative second practice session at the Marina Bay circuit on Friday third quickest behind the pace-setting Ferraris of Carlos Sainz and Charles Leclerc.
He said that, while things looked very close between a number of teams and more was needed for qualifying, it had been a hugely encouraging run for Mercedes.
"It's definitely probably our best Friday of the year so far," explained Russell. "But it is definitely really close between probably five teams at the moment, which is pretty exciting.
"So we will have to work hard overnight, and try and gain those last milliseconds ahead of tomorrow."
While it was a surprise for many to see Ferrari at the front on the high-downforce Singapore track, Russell suspected that the squad could not only maintain that form into Saturday but could actually go quicker based on GPS analysis of what engine modes it was running.
"Ferrari are looking favourites at the moment and I don't think they were maximum [with their] power unit as well," added Russell. "They've probably got a couple more tenths in the pocket.
"The fight is probably for the second row. But we never know what's going to happen.
"The tyres are going to be key: when we have the C5, the softest compound, just getting it in the sweet spot you can find tenths of a second so easily.
"So we just need to find that sweet spot, try to nail every single lap and find ourselves in a good position."
Russell's optimism about the day was shared by team-mate Lewis Hamilton, who concurred it had been the most encouraging Friday of the year after he ended FP2 in fifth spot.
"FP1 was solid," he said. "We were still a little bit off where we wanted to be, but it wasn't too bad. FP2 was for sure the best FP2 session I've had this year.
"It was nice to finish a Friday feeling so positive. I think we've got a good platform to build off for the rest of the weekend. It's the best I've felt from a Friday this year, so I hope we can do some good work overnight, as we always tend to do, and continue to improve."
Russell's remarks about Ferrari's speed being genuine were echoed by Aston Martin's Fernando Alonso.
The Spaniard, who ended up fourth in FP2, thinks the Maranello team are clearly ahead – as he also anticipated a better Saturday for the struggling Red Bull team.
"I think Ferrari is probably out of reach again," explained Alonso. "Like Monza, they are a little bit too fast.
"Red Bull will be fast tomorrow when it counts, so yeah, it's very tight. You can be P5 or P6, or you can be out of Q3 because within two tenths there are a lot of cars. It's going to be tight. We have to be ready for anything and nail the lap in Q2 and Q3."
Additional reporting by Adam Cooper
