The Finn clocked a best lap in one minute and 16.785 seconds to outpace the six-time champion by 0.039sec with last Sunday’s race victor Max Verstappen third for Red Bull, nine-tenths adrift of the fastest time.
The Dutchman had beaten both Mercedes men to claim the ninth win of his career in the 70th Anniversary Grand Prix in sweltering conditions at Silverstone.
But with the temperature hovering at 28 degrees on a perfect summer’s day at the Circuit de Catalunya there were no major heating or tyre issues for the ‘black arrows’ this time out.
Charles Leclerc finished fourth ahead of his Ferrari team-mate Sebastian Vettel, running in a new chassis, Romain Grosjean of Haas and Sergio Perez of Racing Point.
Mexican Perez was back in action after missing both Silverstone races due to coronavirus.
Alex Albon was eighth in the second Red Bull ahead of Kevin Magnussen in the second Haas and Lance Stroll in the second Racing Point.
The session was run in near-ideal conditions and delivered few incidents apart from complaints by Hamilton about his left-front tyre wearing rapidly and his team-mate’s radio communications reverting to a crackle.