Max Verstappen gave Lewis Hamilton and Mercedes food for thought after setting a daunting pace in second practice for the Mexico City Grand Prix.
There was little to separate the two F1 title rivals following FP1 at the Autodromo Hermanos Rodriguez, but in the second hour-long session, Verstappen and Red Bull underlined their apparent superiority at present and on this track high above sea level.
Verstappen finished with a time of one minute 17.301s, a remarkable half-a-second quicker than Hamilton, who can claim the start of his lap was not as clean as he would have liked, but regardless, the gap was an eye-opening one.
The only saving grace for Hamilton, who goes into this weekend 12 points adrift of Verstappen in the drivers' standings, is that team-mate Valtteri Bottas was second fastest, with his time 0.424s behind the Dutch driver set on 10-laps-old softs.
That suggests there is time to spare in the Mercedes, but conversely, how much quicker can Verstappen improve?
Verstappen had earlier also set the early benchmark on the medium tyres with a lap of 1:18.206s, over a tenth-of-a-second quicker than Bottas' best from first practice.
The track, however, was improving all the time given the dusty conditions that had prevailed at a venue that had not been used for motor racing for at least 18 months.
After improving to a 1:17.920s on the medium, Verstappen then set the timing screen alight once he switched to the soft compound, improving by six-tenths of a second to his 1:17.301s.
It was a delightful session for Verstappen, whereas Hamilton endured a wretched opening 15 minutes on a set of hard tyres, with the seven-time champion initially getting snarled up with the Alfa Romeos of Kimi Raikkonen and Antonio Giovinazzi as traffic played havoc early on.
Once Hamilton finally set a timed lap, that was just over six-tenths of a second adrift of Verstappen's opener, it was swiftly deleted as it was completed with double-waved yellow flags flying.
On Hamilton's next lap, he was forced to take to the run-off area between turns one and two, as was the case in first practice at one stage.
Unlike in that session, however, Hamilton correctly navigated his return to the track by going to the left of a bollard at turn three. Failing to do so in FP1 earned him a reprimand from the stewards.
It leaves Hamilton and Mercedes with seemingly plenty of work to do going into final practice and qualifying to avoid Verstappen likely to stretch his advantage on Sunday.
Home hero Sergio Perez, who had crashed and damaged the rear wing of his RB16B in FP1, was fourth quickest, just 0.061s behind Hamilton.
At the moment, there is no team capable of challenging Red Bull and Mercedes, with Ferrari's Carlos Sainz fifth quickest, but a second behind Verstappen.
AlphaTauri's Pierre Gasly provided the filling between a Ferrari sandwich as he separated Sainz and team-mate Charles Leclerc, who was 1.304s adrift.
AlphaTauri's Yuki Tsunoda, who will start at the back of the grid alongside Aston Martin's Lance Stroll due to power unit penalties, was eighth fastest ahead of the second Aston Martin of Sebastian Vettel and Alpine's Fernando Alonso.
On a tough day for McLaren, Lando Norris was only 12th on the timesheet, with team-mate Daniel Ricciardo 15th, with his session cut short by an issue with his Friday gearbox.
Williams' George Russell also encountered his own gearbox issues and was left propping up the standings without a time to his name.
The Briton was late to take to the track initially, and when he did finally make an appearance, he quickly reported the gearbox problem.
Initially, it appeared as if a rear body cover screw that had fallen out as Russell pulled out of the garage may have been at fault.
But Williams dismissed the notion, insisting it was an internal gearbox issue that is currently under investigation.