Lewis Hamilton established himself as favourite for his fifth Formula 1 pole position of 2014 by topping Saturday morning practice in Monaco.
The Briton lagged 0.130 seconds behind Mercedes team-mate Nico Rosberg in the first part of the session, when all drivers were lapping on the slower soft-compound Pirellis.
But Hamilton was the first of the pair to head out on super-soft rubber for his qualifying simulation, doing so with 10 minutes to go.
By then, Red Bull pairing Daniel Ricciardo and Sebastian Vettel had already jumped to first and second place respective on their option tyre runs.
The Australian was four tenths faster than Vettel, although the latter had looked set to improve on a later lap before being held up by having to pass Felipe Massa's Williams at Rascasse.
Hamilton then went fastest with five minutes to go, albeit just half a tenth faster than Ricciardo, and appeared likely to improve again before locking up and straightlining the chicane.
Rosberg, who was the last driver to head out on super-softs, left his best lap until late in the session.
He looked set to retake top spot on his penultimate lap, setting the fastest time of all in sector one and then a personal best in sector two, but a slow final sector meant he ended up third behind Ricciardo, 0.116s slower than Hamilton.
Vettel held on to fourth place ahead of Fernando Alonso, the latter lapping just two hundredths of a second quicker than Ferrari team-mate Kimi Raikkonen.
Force India opted to sit out the first part of the session and was the last to hit the track, with Sergio Perez ending up a strong seventh fastest ahead of team-mate Nico Hulkenberg.
Jean-Eric Vergne, who made visits to the run-off area at both Ste Devote and Mirabeau in the closing stages of the session, was ninth ahead of Toro Rosso team-mate and Monaco rookie Daniil Kvyat.
McLaren's troubles continued, with Kevin Magnussen and Jenson Button 11th and 12th, while Williams also disappointed with Valtteri Bottas and Felipe Massa 13th and 14th.
Lotus struggled too, with Romain Grosjean and Pastor Maldonado 16th and 18th, sandwiching Jules Bianchi's Marussia, which showed impressive pace that potentially gives him the chance to challenge for a Q2 position.
Marcus Ericsson was slowest after a difficult session during which he visited the Ste Devote escape road, having to reverse onto the track, and also survived a brush with the barrier.
Pos Driver Team Time Gap Laps
1. Lewis Hamilton Mercedes 1m16.758s 27
2. Daniel Ricciardo Red Bull-Renault 1m16.808s +0.050s 26
3. Nico Rosberg Mercedes 1m16.874s +0.116s 24
4. Sebastian Vettel Red Bull-Renault 1m17.184s +0.426s 23
5. Fernando Alonso Ferrari 1m17.428s +0.670s 22
6. Kimi Raikkonen Ferrari 1m17.448s +0.690s 24
7. Sergio Perez Force India-Mercedes 1m17.725s +0.967s 23
8. Nico Hulkenberg Force India-Mercedes 1m18.074s +1.316s 21
9. Jean-Eric Vergne Toro Rosso-Renault 1m18.136s +1.378s 19
10. Daniil Kvyat Toro Rosso-Renault 1m18.166s +1.408s 26
11. Kevin Magnussen McLaren-Mercedes 1m18.249s +1.491s 28
12. Jenson Button McLaren-Mercedes 1m18.262s +1.504s 21
13. Valtteri Bottas Williams-Mercedes 1m18.430s +1.672s 31
14. Felipe Massa Williams-Mercedes 1m18.542s +1.784s 30
15. Adrian Sutil Sauber-Ferrari 1m18.598s +1.840s 24
16. Romain Grosjean Lotus-Renault 1m18.776s +2.018s 26
17. Jules Bianchi Marussia-Ferrari 1m18.872s +2.114s 23
18. Pastor Maldonado Lotus-Renault 1m19.118s +2.360s 28
19. Esteban Gutierrez Sauber-Ferrari 1m19.149s +2.391s 28
20. Kamui Kobayashi Caterham-Renault 1m20.271s +3.513s 32
21. Max Chilton Marussia-Ferrari 1m20.394s +3.636s 25
22. Marcus Ericsson Caterham-Renault 1m20.589s +3.831s 30