Lando Norris edged fellow Briton George Russell by just 0.009s to top second practice on Friday for the Barcelona-Catalunya Formula One Grand Prix.
Reigning world champion Norris, who sat out the opening session, and his teammate Oscar Piastri sandwiched the Mercedes driver for the top three, with the Australian coming in 0.057s off the top time.
Italian teenage sensation Kimi Antonelli, who leads the championship after five straight triumphs in the other Mercedes, came in fifth, over half a second behind Norris, with Charles Leclerc fourth in his upgraded Ferrari.
Piastri, who came second in the opening practice and triumphed in Barcelona last year, set an early time to beat of 1:15.724, already ahead of the best morning time as McLaren flexed their muscles.
Russell, who was quickest in the opening session on a hot, sunny day in Barcelona, with track temperatures up at 50 degrees centigrade, was soon on his tail, two 10ths of a second behind.
The 28-year-old is competing in his 100th Grand Prix for the Silver Arrows and two strong practice sessions are encouraging after his troubled start to the season.
Racing Bulls' Liam Lawson pulled up in the pit exit lane after losing power because of a suspected gearbox issue, with the virtual safety car deployed.
Several teams used that time to bolt on the softs, including Mercedes, and midway through the session Russell zipped into the lead by 0.289 seconds, with Antonelli half a second behind.
Norris, who did not finish the previous two GPs in Canada and Monaco, claimed top spot with a blistering 1:15.426 as McLaren showed their battle with Mercedes this weekend will be one to watch.
"Brake pedal feels horrible," Antonelli told his pit wall, while his front left tyre was also worn down.
WARNING FOR PEREZ
Ferrari's Lewis Hamilton, who was ninth quickest, also noted how degraded the tyres were, which could be a big factor this weekend in the heat.
Four-time world champion Max Verstappen was sixth, while Racing Bulls' Arvid Lindblad and Gabriel Bortoleto in an Audi came in seventh and eighth, respectively.
Isack Hadjar was 10th and unimpressed with Sergio Perez, who forced him into the grass to avoid contact, resulting in a warning for the Mexican.
In the opening session, several regulars gave up their seats for rookies, with Leo Fornaroli and Paul Aron impressing.
Alpine's Pierre Gasly was boosted by the news that his third-place finish in Monaco was reinstated but struggled in 17th on the timesheet in the morning, only improving to 16th later on.
Home favourite and two-time world champion Fernando Alonso, who said he is probably racing in Barcelona for the last time, was 21st in his Aston Martin in the afternoon.