Ferrari driver Carlos Sainz of Spain pulls onto the track during the Formula One first practice session at the Monaco racetrack, in Monaco, Friday, May 26, 2023. The Formula One race will be held on Sunday. Photo: AP
Sainz clocked a best lap time in one minute 13.372 seconds beating two-time champion Alonso by more than three-tenths with both running on medium tyres.
Seven-time champion Lewis Hamilton was third in his heavily-revised Mercedes, running a major upgrade package, ahead of Sergio Perez in the leading Red Bull and local hero Charles Leclerc in the second Ferrari.
Defending two-time champion and series leader Max Verstappen struggled in the other Red Bull and was sixth ahead of Lando Norris of McLaren, Esteban Ocon of Alpine and Lance Stroll in the second Aston Martin.
George Russell was unable to build confidence in the second revamped Mercedes car and was 16th.
The session was run on a bright and blue-skied day in the Mediterranean principality, Norris clocking an early quickest time for McLaren, on medium tyres, as the field began gingerly in perfect conditions.
Leclerc slotted into second behind him for Ferrari, but Verstappen was finding problems as he struggled with his Red Bull.
"The clutch is almost impossible out of the pits," he said.
"And the car is bottoming a lot… It’s very difficult to drive."
Sainz, like Leclerc, running mediums in the second Ferrari, had a brush with the barriers, but survived to go top after 10 minutes in 1:15.198 as the lap times tumbled.
The Monegasque driver was the first into the 1:14's before Hamilton, having switched to mediums, went top in 1:14.035 to move ahead of Sainz and Norris after half an hour.
This was a boost for the Mercedes team, having introduced a major upgrades package in a bid to revive their fortunes with a new design philosophy, reverting to normal side pods.
The first red flag of the weekend came after 38 minutes when Nico Hulkenberg lost control of his Haas as he came out of the tunnel and spun.
It was a brief pause before the action resumed, Alonso delivering a clear reminder of his and Aston Martin’s potential to create an upset and end Red Bull's domination in 1:13.907.
Fellow-Spaniard Sainz wasted no time in responding in 1:13.690 before Hamilton and Verstappen shared a 'moment' as they came out of the tunnel, the Briton easing to allow the Dutchman to pass, but both cutting the Nouvelle Chicane in the process.
This minor thrill was surpassed when Alex Albon hit the barriers at Saint Devote in his Williams, triggering a second red flag stoppage that ended the session.
"Yes, I’m ok," a dazed-sounding Albon said.
F1 is returning for the seventh round of the championship after last weekend's Emilia Romagna Grand Prix at Imola was cancelled due to the disastrous flooding in the region.
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