Mercedes driver Nico Rosberg played down his advantage over team-mate Lewis Hamilton during the second practice session for the Brazilian Grand Prix.
Rosberg, who won the race in 2014, finished almost half a second clear of Hamilton in the second 90 minute session at Interlagos but believes different engine settings accounts for the difference.
"It was a good day, as we were able to test a few new things in the first session," he said.
"Times in the afternoon were not showing the real picture, as Lewis drove in different engine modes to me.
"He was also very quick today and it looks like we will have a great battle again this weekend. Besides this, we also had to learn the track because there are some quite major changes with the new kerbs."
Hamilton was encouraged by the feel of his Mercedes W06 Hybrid around Interlagos' short lap.
"The car feels good here - but I think it's going to be a close, hard-fought weekend," he explained.
"Last year in the race I had really good pace - but it's hard trying to find the right balance that works in qualifying and the race.
"I really need to improve my grid position this time because that can heavily influence the race. It's a short lap, it's hot and humid here and the track is also hard on the tyres.
"But they're working well and the grip is good. There is a bit of degradation but not as much as usual, so its generally feeling very good out there."