It was Russell that benefitted the most from the W15 as he came out second fastest in the session, two tenths behind Fernando Alonso.
Meanwhile, Hamilton was the subject of an investigation by the stewards after the session following a near-miss with Logan Sargeant .
Hamilton bemoans 'difficult day' in Saudi Arabia
The Williams driver was forced to take evasive action at turn 11 after he encountered the slow-moving Mercedes in the middle of the track; an incident the FIA deemed what would have been a “serious, high speed crash.”
As a result, Hamilton was issued with a warning and Mercedes were fined 15,000 euros (£12,800) for not informing the Brit Sargeant was there, capping off a dismal day for the 39-year-old.
Reflecting on his day on the track, Hamilton told Sky Sports: "A difficult day. Just lacking confidence in the rear of the car and the set-up.
"We did some work from session to session, changed the car quite a bit, but the underlying issue with the rear end that I was struggling with.
"So I had a couple of really big moments out there. In these high-speed areas you need to have full faith in the rear of the car, and I've just not got that yet."
"We're going to have to go through the data and stuff, but George is obviously a lot happier with his car," he added.
"We kind of went in different directions today. We're all trying different things to try to find the right solution for the car.
"But yeah, all I want is a stable rear, and then I'll be happy. So that's what I'm working on."