The Monegasque driver, who won twice for Trident in his 2011 campaign, took advantage of a drying afternoon track to set the overall best, a 1m29.868s, in the closing stages.
That was enough to edge out Felipe Nasr and 2012 Formula Renault 3.5 champion Robin Frijns, once again testing for Trident.
Frijns, who had been the first of the trio to break under the 1m30s barrier, was less than one tenth of a second back from Coletti.
James Calado finished fourth fastest overall for ART and also ended comfortably top of a wet morning session.
His best effort, while some 20s slower than the afternoon, still put him almost a second clear of a chasing pack led by Daniel de Jong and Simon Trummer.
Halfway through the morning Tom Dillmann had gone quickest for newcomer Russian Time, testing for the first time after acquiring iSport's GP2 entry.
The poor morning conditions led to three stoppages. Rio Haryanto clipped the Turn 2 barrier and Kevin Giovesi stopped at Turn 8 in the first hour of running, while simultaneous offs for Rodolfo Gonzalez and Ma Qing Hua brought the morning to a slightly premature close.
GP3 race-winner Conor Daly was in action for the new Hilmer team, with which Dillmann had set the pace at Jerez last week.
- Sports & Recreation
- Robin Frijns
- Felipe Nasr