Carlos Sainz topped the opening session for this weekend's Monaco Grand Prix, the Ferrari driver exploiting his car's pace in the track's middle sector and edging Aston Martin's Fernando Alonso and Mercedes' Lewis Hamilton.
The first practice concluded prematurely with a few minutes left on the clock when Williams' Alex Albon clouted the barriers on the exit of Ste Devote and brought the red flag.
Red Bull's Sergio Perez - last years' winner in Monte Carlo - and Max Verstappen ended FP1 respectively P4 and P6, with local hero Charles Leclerc slotting in fifth.
Times to follow…
The cancellation of last week's Emilia Romagna Grand Prix means that teams are running a raft of upgrades in Monaco this weekend, with Mercedes' new-spec W14 the center of attention of many photographers in the pitlane.
But over at McLaren there was a cosmetic change to the team's MCL60 which took to the track adorned with a special Triple Crown livery celebrating the manufacturer's past wins in Monaco, at Indianapolis and at Le Mans.
As the track went green, hard tyres were the preferred choice for most of the field, although Ferrari's drivers and Lando Norris opted for mediums at the outset.
Leclerc and Sainz were fastest in the early stages of the session, the pair edging Verstappen who unhappily noted that his RB19 was bottoming excessively around the track.
Leclerc became the first driver to dip under the 1m15s mark, but Sainz, Alonso and Verstappen all followed suit.
As the track rubbered in, lap times marginally improved. But over at Williams, Logan Sargeant was seen limping out of the tunnel and back to the pits, the FW45 suffering from an apparent drive issue.
After a leisurely start to their session, Mercedes' chargers upped the pace, with a medium-shod Hamilton going top and setting a new benchmark time of 1m14.035 as the session reached it halfway point.
However, teammate George Russell complained of difficulties in switching his tyres on and of a sliding rear end.
Meanwhile, Verstappen reported feeling a bit more comfortable onboard his car after Red Bull tweaked the RB19's set-up to dial out its bottoming.
The track claimed its first casually of the weekend when Nico Hulkenberg hit the inside barrier at the chicane which spun the Haas around and inflicted a rear left puncture.
The mishap brought out a brief red flag to allow marshals to collect a bit of small debris thrown off the German's car.
Practice resumed with 20 minutes left on the clock and with Alonso taking charge with the first sub 1m13s lap of the day. The Spaniard thus bumped Hamilton down to second while Perez jumped to third.
But Sainz quickly stole his countryman's thunder with a 1m13.690s that propelled the Ferrari driver to the top.
In an attempt to snatch back the top spot Alonso stumbled upon a slow-moving Perez on the racing line into Casino Square, and the two-time world champion was anything but happy with the Mexican's antics and promising retaliation.
With just four minutes to go, Alex Albon brought out a second red flag – and a premature conclusion to the session – when the Williams driver lost the rear on the exit of Ste Devote and tore off both left hand corners off his car.
Sainz therefore topped the session which augurs well for Ferrari, while Alonso and Hamilton right behind also showing good form.
Perez and Leclerc completed the top five, with Verstappen, Norris, Ocon, Stroll and Albon rounding off the top ten.
Friday's second practice session will kick off at 17h00 CET.
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