Lewis Hamilton set the pace in second practice at the Singapore Grand Prix as title rival Nico Rosberg failed to record a time on the faster tyre.
Rosberg was on a flying lap on the 'super-soft' tyre when the session was stopped following a heavy crash by Lotus driver Pastor Maldonado.
The German decided not to try again in order to focus on race preparation, leaving Hamilton top, 0.133 seconds quicker than Ferrari's Fernando Alonso.
Red Bull's Daniel Ricciardo was third.
Rosberg was 13th fastest with the time he set on the harder 'soft' tyre.
But the German was just under 0.1secs quicker than Hamilton's best time in the first sector on the lap he had to abort, which suggests the battle between the two will be close once again.
Rosberg leads Hamilton - who expects the battle between the two to be "intense" this weekend - by 22 points in the championship with six races remaining and a maximum of 175 points still available.
Singapore is cited by the drivers as arguably the toughest race of the season, with a long lap on a bumpy track in high temperatures and humidity, and a race that tends to run close to the two-hour maximum.
After the first session, Mercedes engineers had calculated they had an advantage of about 0.6secs a lap over Red Bull but it appeared significantly closer in the later session.
Ricciardo was only 0.3secs adrift of Hamilton's fastest lap - and on race pace the two Mercedes drivers and Ricciardo looked quite closely matched.
Alonso may also be in the fight with Red Bull for the final podium place. His fastest lap was far from his maximum, as it was set on his second flying lap on his super-soft tyres, when the tyres are past their best, after an earlier, faster lap was ruined by a poor final sector.
Red Bull's world champion Sebastian Vettel only ran for the last 15 minutes of the session because the team needed to change an engine that failed at the end of the first session.
The world champion set the fifth fastest time, 0.01secs slower than Ferrari's Kimi Raikkonen, on his late run on super-soft tyres.
The McLarens of Kevin Magnussen and Jenson Button were sixth and seventh ahead of the Force Indias of Sergio Perez and Nico Hulkenberg and the Toro Rossos of Daniil Kvyat and Jean-Eric Vergne.
Williams, who come to Singapore on the back of a run of podium finishes, appeared to be lacking pace on a track where ultimate downforce is key to lap time and Felipe Massa and Valtteri Bottas were down in 17th and 18th places.
Although a number of drivers flirted with the walls, Maldonado's was the only crash of the session.
The accident-prone Venezuelan was too fast through Turn 10, in front of the Singapore Supreme Court, and lost the rear, sliding into the barriers and causing extensive damage to the right-hand side of the car.