(AFP) - Red Bull's Daniil Kvyat stole the limelight and upstaged record-seeking Lewis Hamilton when he timed quickest in smog-hit second free practice for the Singapore Grand Prix on Friday.
The 21-year-old Russian was the surprise pace-setter with a leading time of 1min 46.142sec at the Marina Bay Street Circuit, ahead of Ferrari's Kimi Raikkonen.
Daniel Ricciardo was third quickest in the second Red Bull with Hamilton, bidding to equal a clutch of milestones set by the late Ayrton Senna, down in fourth on the timesheets.
The unusual make-up of the leader board, in a season dominated by the Mercedes cars of Hamilton and Nico Rosberg, hints at an unpredictable weekend in prospect.
"We're not happy with the performance today," fumed Mercedes boss Toto Wolff. "We haven't really made the tyre in the way we should on the one-lap performance or the long run either.
"We've seen some spectacular performances on the long runs from Red Bull. We just need to get our heads together and assess what's happening."
Championship leader Hamilton is trying equal Senna's record of eight straight pole positions as well as the late Brazilian's career tally of 41 wins from 161 races.
The Briton leads the standings by 53 points from Rosberg, putting him well on course to match his boyhood idol Senna's haul of three world titles.
Haze caused by South-east Asian forest fires was measured at unhealthy levels during Friday's practice sessions, held under floodlights at the downtown layout.
The smog could cause concern for the weekend, after Jenson Button warned earlier of the potential health risks of strenuous driving in polluted air.
Kvyat took control early in the second session and held firm despite losing his cool and swearing at Romain Grosjean when he found himself blocked by the Lotus man.
Hamilton calmly drove hands-free as he adjusted his gloves in the first session but his evening didn't go smoothly with errors taking him off-course in both runs.
Ferrari's Sebastian Vettel, lying third in the championship, timed fifth fastest behind Hamilton, with Force India's Sergio Perez sixth and Rosberg seventh.
American Alexander Rossi, brought in by Manor at the last minute, had a tough debut when he smashed into the barriers late in the first session, leaving his right-side wheels askew.
But Rossi, who has chosen 53 as his race number in honour of movie car "Herbie", recovered in the second run and finished above his bottom-placed team-mate Will Stevens, who also crashed in the later session.