Mercedes' encouraging start to the Las Vegas Grand Prix weekend continued as George Russell topped a final practice session that was effectively brought to a premature end when Lance Stroll stopped on track.
Stroll parked his Aston Martin with six and a half minutes left in the session after it shut down exiting the Turn 12 left-hander onto the back straight, with the red light above its airbox flashing red to indicate its ERS system had not been neutralised.
The Aston was wheeled behind the barriers before the end of the session and the session did resume, albeit only allowing drivers to complete outlaps and practice starts on the grid.
But while that late red flag deprived the field of their final runs, the stage appears to be set for a four-way scrap for pole position between Mercedes, McLaren, Ferrari and Red Bull - with all four cars in the top five come the end of FP3.
It's Mercedes that appears to be in the pound seat, as its form on Thursday in similarly cool conditions indicated, with Russell and team-mate Lewis Hamilton trading fastest times for some time.
It took until midway through the 60-minute session for the first laps close to anything representative to be set, but even then Haas driver Kevin Magnussen's 1m35.625s was almost two seconds off Hamilton's Thursday practice best.
Magnussen spent further spells at the top of the times - as he looks to continue a strong end to his Haas (and, likely, F1) career in a rich vein of form - before the Mercedes drivers hit the front.
Hamilton appeared to have a slight edge as he and Russell chipped away at the fastest time, but Russell ultimately ended the session fastest after completing two flying laps on a second set of soft tyres.
His first effort was beaten by Max Verstappen and subsequently Carlos Sainz, but Russell's second push lap beat those times comfortably - a 1m33.570s representing the fastest lap of the Las Vegas GP weekend so far.
That gave Mercedes a clean sweep of fastest practice times, Hamilton having been fastest in both Thursday practice sessions.
Oscar Piastri also usurped Sainz before the red flag, lapping 0.215s off Russell, with Lando Norris a tenth the other side of Sainz's Ferrari in fourth.
Red Bull spent the first part of the session running exclusively on medium compound tyres, with both drivers complaining about grip and the track conditions.
Points leader Max Verstappen, who can wrap up a fourth F1 title this weekend, complained towards the end of his running that the grip was "only getting worse" and that his RB20 was "undriveable" as he ran deep twice in two laps at the Turn 5 right-hander.
"I can't drive it. I'm going to crash. My left front is completely f***ed," he added.
But once on softs he was far happier - "grip is miles better" - and briefly went fastest with what was at the time a fastest middle sector of all - the RB20's pace through that part of the lap offsetting any drag disadvantage Red Bull is carrying without a specific ultra-low downforce rear wing for Las Vegas.
He ended the session fifth and 0.567s down on Russell, though that gap was exaggerated by Verstappen being denied a second push lap on that set of softs.
Hamilton did not get a second soft-shod run in and ended up sixth ahead of Williams duo Alex Albon and Franco Colapinto, with Magnussen shuffled down to ninth and Pierre Gasly completing the top 10 for Alpine.
Like Red Bull team-mate Verstappen, Sergio Perez was busy over the team radio in the early stages of the session, reporting at various times that the track was "nowhere" and "miles off".
He ultimately ended up 13th and 1.491s off Russell, albeit again with the caveat that he was unable to complete a second push lap on softs.
Perez also failed to reach the end of the pitlane in time at the end of the session to make it out on track for a final practice start.
