Ferrari's Kimi Raikkonen led Lewis Hamilton's Mercedes by just 0.011 seconds in second practice at the Singapore Grand Prix.
Hamilton's title rival Sebastian Vettel was ninth after hitting the wall and damaging his car's right-rear corner.
Vettel was one corner from the end of a lap that looked set to put him up with Raikkonen and Hamilton.
The German was able to get the car back to the pits but the extent of the damage ended his session.
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Vettel slid sideways into the wall on the exit of Turn 21, at the end of what would have been his fastest lap of the season, catching it with his right-rear wheel.
It was a glancing blow and the wheel stayed attached to the car but he immediately felt damage and pulled straight into the pit entry.
As he parked in the Ferrari pit, hydraulic fluid was pouring from the back of the car.
"We lost some time, which is not ideal, but nevertheless the feel I had for the car was all right and we should be fine for tomorrow," said Vettel, who is 30 points behind Hamilton with seven races to go.
"It was very close and I expect it to be very close tomorrow."
The four-time world champion was the second driver to fall foul of the unyielding concrete walls. Sauber's Charles Leclerc, whose promotion to Ferrari as Vettel's team-mate next season was announced this week, crashed in first practice.
Leclerc, who has never raced at Singapore before, wiped off his car's right-front wheel and suspension but it was repaired in time for the second session, in which he was 14th fastest, two places and 0.25secs slower than team-mate Marcus Ericsson.
Ferrari came into the weekend as favourites on a track where Mercedes have traditionally struggled.
Hamilton said on Thursday that he "hoped" Mercedes would be competitive but that "Ferrari should have the upper-hand".
Ferrari may have ended the day quickest, but the Mercedes was much closer to it on pace than had been expected - both in qualifying trim and later in the session on race fuel loads.
Raikkonen and Hamilton were very evenly matched on their race-simulation runs. Hamilton ended his run on the hyper-soft tyres on which teams are likely to start the race with a slightly quicker average lap time than the Finn.
But it was difficult to be absolutely sure of the relative pace of the cars because Hamilton punctuated his run with a number of slow laps that might have helped the longevity of his tyres.
Max Verstappen was third fastest for Red Bull ahead of team-mate Daniel Ricciardo. The Dutchman was 0.522secs off the pace but Red Bull appeared to be much closer on race pace, Ricciardo setting an average 0.064secs quicker than Hamilton but on a slightly shorter run.
The second Mercedes of Valtteri Bottas was off the pace - 0.669secs slower than Hamilton.
Best of the rest was Renault's Carlos Sainz, ahead of Haas' Romain Grosjean and the McLaren of Fernando Alonso, an encouraging start for the Spanish double world champion on a track where he has always excelled.
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