MP Motorsport driver and Alpine Academy member Martins, who won last year’s Formula Renault Eurocup championship, topped the time sheets with a 1m31.743s set during the afternoon session.
He led from Doohan, with ART GP driver and Mercedes junior Frederik Vesti in third.
Trident’s Clement Novalak came fourth, followed by Hitech’s Jak Crawford and Charouz driver Michael Belov, competing in his second year of F3.
ART Grand Prix’s Juan Manuel Correa, in just his third session back in motorsport since surviving a tragic multiple car Formula 2 crash at Spa in 2019 that claimed the life of Anthoine Hubert, set a time of 1m33.013s, placing him 18th overall – the same position as during the last test in Austria.
The 30-strong field assembled at the Circuit de Catalunya-Barcelona for the second round of testing on Wednesday, after an earlier test at the Red Bull Ring ahead of the 21-race season.
After a damp start to the day, Crawford led the morning session with a quickest time of 1m33.674.
He was followed by Jenzer Motorsport’s Pierre-Louis Chovet and Carlin rookie Kaylen Frederick, with the latter’s teammate Jonny Edgar ending the run fourth quickest.
Running on Wednesday and Thursday, the two days of testing is split into a morning and afternoon session, with a total of 12 hours of track time available.
Teams are testing on Pirelli’s P Zero hard tyres, the same compound that the drivers will race on at the opening round next month.
The two days of track time came at the circuit that will host the 2021 season opener, alongside the Formula 1 Spanish Grand Prix, from May 7-9.
There will also be a third round of testing following the first race, this time at the Jerez circuit on May 12-13.