The 18-year-old, back in the cockpit for the first time since his record-breaking victory at the Spanish circuit, worked his way down to a 1m 23.267s, as Renault's upgraded engine continued to offer plenty of promise.
Stoffel Vandoorne backed up McLaren's strong showing by going second fastest, the reserve driver spending much of the morning completing a number of different aerodynamic tests on the MP4-31.
Daniil Kvyat meanwhile put Toro Rosso third, the Russian finishing several tenths of a second down the road in what was his first test since his shock return to the team.
Pascal Wehrlein, a late call up for Mercedes, put the Silver Arrows fifth, fractionally slower than Kevin Magnussen's Renault.
At Ferrari, meanwhile, Antonio Fuoco took over the reigns from Sebastian Vettel, and put the Scuderia seventh. Force India and Manor also made use of their young driver roster - Alfonso Celis was eighth fastest for the former, while current GP2 racer Jordan King rounded out the timesheet for the latter.
Testing continues this afternoon. You can follow minute-by-minute timing updates on the official F1 App - go to 'Results and Standings' and click 'Test'.
Unofficial morning test times from Spain
|1||Max Verstappen||Red Bull||1:23.267||65|
|3||Daniil Kvyat||Toro Rosso||1:24.737||1.470||68|
|8||Alfonso Celis||Force India||1:26.855||3.588||37|
Formula1.com will bring you full session reports at the end of each day's running at Barcelona.