Nico Rosberg turned the tables on Mercedes team-mate Lewis Hamilton to top second practice at the season-ending Abu Dhabi Grand Prix.
Hamilton had been fastest by 0.141 seconds in the first session, but Rosberg pipped the world champion by 0.138secs in the second session.
The two Mercedes were well clear of the rest of the field, headed by Force India's Sergio Perez, 0.627secs back.
Red Bull's Daniel Ricciardo was fourth, ahead of Ferrari's Sebastian Vettel.
While Mercedes appear untouchable on one-lap pace, there were hints that Ferrari might be able to take the fight to them in the race.
Ferrari are often more competitive relative to the champions when the softer of the tyres are in use - as they are this weekend with the grippiest combination of soft and super-soft.
Kimi Raikkonen looked especially competitive, making the super-softs last particularly well for a long run that on average was as fast as Rosberg's, despite being twice as long.
Rosberg said he was on the back foot for the weekend because he was using an engine that had a higher mileage than the one in Hamilton's car.
This is because he suffered an engine failure at the Italian Grand Prix back in September that put him out of sync on engine usage.
"It has been a good start to the weekend, even though Lewis did not show his pace on one lap. It is clear that he still has some reserve," he said. "Today is not the real picture.
"In general it is going to be difficult because I have an extremely old engine - the one I have has a lot of miles on and that is costing me straight-line speed.
"So it is going to be a difficult weekend as a result. I just have to go quicker in the corners."