Lewis Hamilton hit back at title rival Max Verstappen to top the time sheets at the end of the first day’s action for Abu Dhabi’s championship showdown Grand Prix.
But when the flag fell after dark for second practice, it was the seven-time champion who got his nose in front.
And there was a whopping 0.6 seconds to his Red Bull rival in fourth.
As the title rivals turned up the gas, both had laps deleted for going off the track.
Between the duo was Esteban Ocon in second and Mercedes' second driver Valtteri Bottas in third.
That made it one session apiece on the first day for the pair as they prepare for the final round on Sunday.
But there is plenty more to come from both drivers as the practice days are used to set up the car and get used to the redesigned track.
In the early, hour-long session, Mercedes had admitted that they were struggling to set their car up for the new, faster layout.
After 21 rounds of the world championship, they are dead level in points. But Verstappen has a significant advantage.
If the rivals crash out together, as they have twice already this season, it will make the Red Bull racer the champion as the championship will go to a countback on wins — and Verstappen has one more.
But the stewards have specifically said that dubious tactics could be met with a points deduction or even being slapped with a ban for a year or more.
Red Bull boss Christian Horner said on Friday there was everything to play for.
“Mercedes look very competitive here, especially the first two sectors, but we come back to them in the third one.
“But we have 24 hours to come up with a solution.”
And he repeated his plea for consistency in stewarding decisions and punishments because his racer feels he is being unfairly punished by stewards after receiving two time penalties at the last race in Saudi Arabia.
“Again, it just comes back to whether you want consistency of rules” Horner said.
“What happened in Turn 4 [in Brazil], what happened wherever it was, should be applied to this race.
“You can't just go and pluck something out of the air and say, ‘yep, that's what will now apply’. That would make a mockery of the policing of the championship.
“This championship has been a pressure cooker and that’s why we go racing. Max has been just amazing. Let’s see if we can do something a bit magic on Sunday.
“I’ve told the team whatever happens, we can be amazingly proud of what we’ve achieved.”