The Australian's time of one minute 42.489 seconds was a new record and he ended the session 0.109 seconds ahead of Ferrari’s Sebastian Vettel.
Championship leader Lewis Hamilton, who is seeking his third successive victory, was fourth behind Ricciardo’s team mate Max Verstappen. He was 0.415 seconds off Ricciardo's pace.
The Briton, who seized the overall lead from title-rival Vettel after leading Mercedes team mate Valtteri Bottas to a one-two finish in Monza, is expecting a less straightforward weekend in Singapore.
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The tight twists of the circuit are expected to play to Ferrari’s strengths, with the Italian outfit dominant at similar layouts in Monaco and Hungary earlier in the year.
Red Bull are also hoping the circuit masks the power deficiencies of their Tag Heuer-badged Renault engine.
Although the opening session was held in daylight, in contrast to the floodlit conditions the drivers will face during the rest of the weekend, Ricciardo’s pace appear to put Red Bull in the frame for victory.
Sergio Perez was fifth-fastest for Force India. Bottas, who agreed a one-year extension to his Mercedes contract in the build up to the weekend, was sixth. Kimi Raikkonen was seventh in his Ferrari ahead of Fernando Alonso.
The Spaniard’s McLaren outfit has been in the spotlight this week after the team confirmed on Friday that it would be splitting with power-unit supplier Honda at the end of the 2017 season.
Nico Hulkenberg was ninth for Renault ahead of Toro Rosso’s Daniil Kvyat in 10th.
The Russian’s team mate Carlos Sainz, expected to head off to Renault next season as part of the complex engine saga, sat out the session, handing his car to Formula 2 racer Sean Gelael.
The Indonesian was 18th, 3.3 seconds off Kvyat’s pace.
The 90-minute session was uneventful apart from a few lock-ups from drivers as they got to grips with the track.
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Italian Grand Prix
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