Alex Lowes went quickest in World Superbike practice at the Chang International Circuit in Thailand on Friday after Jonathan Rea had set to the early pace.
The Suzuki rider was fastest in the second session with a time of one minute 34.685 seconds, enough to put him clear of Rea in second place.
Rea, who leads the standings on 45 points with Leon Haslam after the opening meeting in Australia, improved on his pace-setting first session time of one minute 35.004secs to finish second ahead of Chaz Davies.
Ducati rider Davies suffered a crash in FP1, but responded by improving by four tenths of a second, with team-mate Haslam in fourth and Tom Sykes fifth.
Defending champion Sylvain Guintoli got better through the day in Buriram and finished in sixth.
Ahead of the two remaining free practice sessions on Saturday, Rea was full of praise for the track ahead of the inaugural Thai race weekend.
"It is just nice to ride on a new track and second it is very safe as there are a lot of run-off areas," he told the WSBK website.
"The first part is like a 'mini-Monza', with the first corner being exactly like Turn 1 at Assen, although it leads to a long straight.
"The complex area in the final section is like a small Qatar. It is a nice circuit, the asphalt is quite smooth apart from turn 1, which is a bit bumpy.
"It is not an easy track, I just learned it a little bit faster."