Vettel, who focused mainly on short run work, set a best time of 1m 23.220s in the afternoon session, which is faster than he went in qualifying at the same circuit last weekend.
The German finished 0.117s quicker than Rosberg, who like Vettel and Renault rookie Esteban Ocon, completed more than 100 laps.
"I think it is a unique chance having the opportunity right after the GP to test at the same track, more or less on the same conditions," said Vettel.
"Saturday we struggled a bit so today we tried some stuff. We needed to have a good look at it, but this is not the only thing we were here for. For sure we tried to cover as much as possible in one day."
McLaren’s Jenson Button – the lunchtime leader – finished the day with the third quickest time after failing to improve on his morning marker of 1m 23.753s, set on the supersoft tyres.
That left him just ahead of Romain Grosjean, who fitted ultrasoft tyres to his Haas late in the afternoon and vaulted up the order as a result.
Manor’s Pascal Wehlein was another to do qualifying simulation work, and finished fifth, just ahead of Red Bull’s Daniel Ricciardo.
Toro Rosso’s Pierre Gasly ended with the quickest time of the four young drivers in attendance, even without the Italian team letting him ‘off the leash’.
“Last year Pierre did a good job for us in the young driver test days and he has done another excellent day for us today,” said Phil Charles, Toro Rosso’s chief race engineer.
“We got most of the planned program completed with a large number of aero characterization runs in the morning and then a set-up program accomplished just after lunch. His runs were consistent and his feedback was concise.
“We were just about to ‘set him off the leash’ for some performance runs at the end of the day when a systems issue stopped the car from running. We are currently looking into it – it’s a pity we could not get to see what Pierre is capable of.”
Fellow GP2 racer Alex Lynn found himself the subject of attention for much of the day after Williams fitted his FW38 with an unusual double-deck rear wing. It is believed the team were running the device in a bid to get a handle on the 2017 aerodynamic regulations.
The first of two in-season tests concludes at Barcelona on Wednesday, when Spanish race winner Max Verstappen is scheduled to be amongst those taking part.
Sauber are the only team not in attendance.
You can follow minute-by-minute timing updates on the official F1 App - go to 'Results and Standings' and click 'Test'.
Unofficial Tuesday test times from Spain
|6||Daniel Ricciardo||Red Bull||1:24.307||1.087||89|
|7||Pierre Gasly||Toro Rosso||1:24.821||1.601||78|
|8||Alfonso Celis||Force India||1:25.467||2.247||99|
Formula1.com will bring you full session reports at the end of each day's running at Barcelona.