George Russell topped the times for Mercedes in Friday's opening practice at this weekend's season-ending Abu Dhabi Grand Prix, outpacing nearest rival Felipe Drugovich of Aston Martin by 0.288 seconds.
Brazilian Drugovich was the outstanding one of the 'rookies' involved as most teams obeyed mandatory guidance to deploy young drivers.
Daniel Ricciardo was third for Alpha Tauri, a tenth adrift, ahead of Alfa Romeo's Valtteri Bottas and Lance Stroll, in the second Aston Martin, and McLaren's Oscar Piastri.
The session was run in hot conditions with an air temperature of 27 degrees Celsius (80.6 degrees Fahrenheit) and the track at 42, near perfect for the final event of an exhausting 22-race season following last weekend's race in Las Vegas.
Ten aspiring young drivers, with minimal Formula One experience, were given their chance to step into cars normally occupied by established drivers.
It was a switch that left three-time champion Max Verstappen, his Red Bull teammate Sergio Perez and Lewis Hamilton of Mercedes among those obliged to sit the session out.
Practice was preceded by confirmation that McLaren have extended their contract to use Mercedes power units until 2030.
"It has been a cornerstone of our motorsport strategy to work with strong customer teams," said Mercedes team chief Toto Wolff in a statement.
"This has many advantages – it gives a clear competitive benchmark, accelerates our technical learning and strengthens the overall F1 business case for Mercedes-Benz."
Mercedes also supply rivals Aston Martin, who plan to switch to Honda engines in 2026, and Williams.
It was also clarified by Red Bull that it was Lewis Hamilton's father Anthony who had contacted Christian Horner earlier this year and not any member of the Mercedes' driver's management team.
"It's a non-story," Horner told SkySports F1.
"Anthony is a nice chap and I have text messages from a lot of people."
Hamilton had denied he or his management spoke to Horner about joining Red Bull alongside Verstappen, suggesting the Red Bull chief had been 'stirring things up' with comments made before arriving in Abu Dhabi.