Ferrari's Carlos Sainz and Charles Leclerc topped the opening practice for this weekend's Mexican Grand Prix, the Scuderia chargers leading the Red Bull duo of Sergio Perez and Max Verstappen.
Lewis Hamilton and Fernando Alonso completed the top six, but only 0.192s separated the group of contenders.
Further down the field, it was a tough session for F1's rookies, with technical issues plaguing part of the group of five young drivers.
The focus on the run-up to Friday's opening practice at the Autodromo Hermanos Rodriguez was on the cost cap breach penalty levied upon Red Bull, which Christian Horner has called "draconian".
But the Milton Keynes-based outfit has taken it on the chin, but there's no doubt we'll be hearing more from Horner and the team's rivals during this weekend.
Five aspiring young champions sprung into action in FP1, with Logan Sargeant returning to Williams, AlphaTauri 2023 recruit Nyck de Vries running with Mercedes in place of George Russell, Pietro Fittipaldi driving for Haas in Kevin Magnussen's seats, Jack Doohan making his public F1 debut onboard Esteban Ocon's Alpine, and Liam Lawson in action with AlphaTauri.
Sebastian Vettel, sporting a retro Red Bull helmet livery in memory of the late Dietrich Mateschitz, led the field out of the pits.
It was a troubled start for Lawson who reported a brake problem that brought the Kiwi immediately back to the Alpine garage for a thorough check.
Fifteen minutes in, Verstappen led proceedings, followed by Perez and Sainz, with a 0.497s spread separating the trio, equipped with Pirelli's hard rubber.
Leclerc had a tardy start to his work session, but the Monegasque's first push lap was good enough for P1, 0.745s quicker than Verstappen. However, the Ferrari charger had achieved his run on the softs.
As more drivers switched to the red-walled compound, the running order swiftly changed at the front although Leclerc remained in charge.
Meanwhile, there appeared to be an issue for Ricciardo whose car was stranded in the McLaren box, the car's crews seen carrying out work.
Shortly after the half-way mark, a grip-less Verstappen indulged in a, inconsequential spin at Turn 10, while Sainz overhauled Leclerc at the front, the Ferrari pair followed by Alonso, Norris and Perez.
With a little over 20 minutes to go, a yellow and then a red flag was deployed as a result of Fittipaldi stopping his Haas - or rather Magnussen's Haas - out on the course in the vicinity of Turn 2, the victim of an apparent power unit related issue if the presence of smoke at the rear of the VF-22 was anything to go by.
The session resumed with 15 minutes left on the clock, and with Mercedes finally kicking into a higher gear, the Brackley squad's W13 fitted with a slightly different new front wing.
Hamilton's first push slotted the Briton among the top five while de Vries remained focus on the team's work programme.
Sadly, Doohan's session ended prematurely due to some suspicious PU data noted by the Alpine's engineers. But over at McLaren, Ricciardo was back in action after a lengthy stay in his team's garage.
It wasn't a good day for the rookies, with Lawson parking his AlphaTauri with four minutes to go and smoke pouring from the front brakes.
The incident brought out the second red flag of the session, which equated to the end of FP1.
It was thus a Ferrari 1-2 followed by a Red Bull 1-2, with Hamilton, Alonso, Bottas, Norris, Gasly and Vettel forming the top ten.
However, there was only a 0.413s spread between the top 8, an exceptionally tight gap that augurs well for this afternoon's second session.
Lawson proved the quickest rookie on track, the Kiwi clocking in P16 and followed by his four youn gun colleagues.
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