Fernando Alonso topped Thursday's rain-affected second free practice session for the Monaco Grand Prix.
Although it did not rain during the 90 minutes of running, a heavy downpour in the hour before soaked the track, leading to a tentative start in terms of track action.
It was not until the final 10 minutes that drivers started posting lap times on slick rubber, with Alonso completing a six-lap stint on super-soft Pirellis and setting his best time of 1m18.482s on his final flier.
With the track getting faster in the final minutes, everyone except Kimi Raikkonen set their fastest time on super-soft rubber, although it did not get fast enough for Alonso to eclipse Lewis Hamilton's fastest time of the morning session.
Hamilton was second fastest, 0.419s slower on the same rubber, with Sebastian Vettel third quickest, just over half a second down.
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Jean-Eric Vergne, who had been the first driver to set a time on slicks with eight minutes remaining on soft rubber, then switched to the faster super-softs and went fourth fastest ahead of Valtteri Bottas.
Bottas was the only driver to head out during the first 38 minutes, completing a single, tentative installation lap on intermediate rubber early on.
Things then livened up, with Monaco debutant Daniil Kvyat the first to post a complete lap to go top briefly before Toro Rosso team-mate Vergne deposed him, with both on intermediate rubber.
The STR duo traded fastest times, initially running in the 1m40s bracket, but soon the best laps on intermediates tumbled in tricky conditions that caught out Kvyat when he had to take to the escape road at Ste Devote.
Eight drivers posted serious times on intermediate rubber before the final 20 minutes of the session, with McLaren's Jenson Button ending up fastest with a best time of 1m31.594s to head Sebastian Vettel by a second.
Raikkonen was the ninth driver to complete a lap during this phase of the running, but it was not a serious attempt thanks to his Ferrari getting stuck in third gear, leading him to return to the pits and end his session prematurely, hence his position 27 seconds off the pace at the foot of the timesheets.
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With conditions improving all the time, intermediate-shod Kevin Magnussen was set to knock his team-mate off top spot after setting the fastest time in the first two sectors before overdoing it into the Turn 15/16 right/left chicane and cutting the track.
His lap was good enough to go second fastest, 0.733s behind Button, but with the track rapidly drying out it was clear that the timesheets would be dominated by laps set on dry-weather rubber.
Despite the tricky conditions, Marcus Ericsson, carrying a Ronnie Peterson helmet livery in tribute to his compatriot's 1973 Monaco GP victory, was the only driver to find the wall.
He nosed his Caterham into the barriers at the exit of Portier in the penultimate minute, but was able to back out and return to the pits.
Pos Driver Team Time Gap Laps
1. Fernando Alonso Ferrari 1m18.482s 15
2. Lewis Hamilton Mercedes 1m18.901s +0.419s 12
3. Sebastian Vettel Red Bull-Renault 1m19.017s +0.535s 15
4. Jean-Eric Vergne Toro Rosso-Renault 1m19.351s +0.869s 14
5. Valtteri Bottas Williams-Mercedes 1m19.421s +0.939s 9
6. Sergio Perez Force India-Mercedes 1m19.668s +1.186s 9
7. Nico Hulkenberg Force India-Mercedes 1m19.712s +1.230s 10
8. Jenson Button McLaren-Mercedes 1m19.721s +1.239s 16
9. Daniel Ricciardo Red Bull-Renault 1m19.779s +1.297s 11
10. Kevin Magnussen McLaren-Mercedes 1m20.230s +1.748s 16
11. Felipe Massa Williams-Mercedes 1m20.394s +1.912s 8
12. Daniil Kvyat Toro Rosso-Renault 1m20.622s +2.140s 13
13. Adrian Sutil Sauber-Ferrari 1m20.811s +2.329s 8
14. Pastor Maldonado Lotus-Renault 1m20.977s +2.495s 7
15. Esteban Gutierrez Sauber-Ferrari 1m21.467s +2.985s 8
16. Romain Grosjean Lotus-Renault 1m21.700s +3.218s 6
17. Kamui Kobayashi Caterham-Renault 1m21.924s +3.442s 6
18. Jules Bianchi Marussia-Ferrari 1m21.937s +3.455s 13
19. Max Chilton Marussia-Ferrari 1m22.683s +4.201s 13
20. Nico Rosberg Mercedes 1m22.862s +4.380s 11
21. Marcus Ericsson Caterham-Renault 1m23.164s +4.682s 6
22. Kimi Raikkonen Ferrari 1m45.509s +27.027s 4