Ahead of today's opening session the air temperature is 26 degrees C, while the track temperature is 29.5 degrees.

The Sky is bright blue, the sun is shining. Welcome to Texas.

Of particular attention will be the circuit's notorious bumps,. Which have previously been a problem for the F1 drivers - remember Vettel in 2019 - and caused havoc at the recent MotoGP event. The organisers claim the issue has been resolved... we're about to find out.

Before the lights have gone green Perez heads out, the Mexican clearly keen to get to work. As he heads out into the sunshine he is followed by Gasly, Schumacher, Ocon, Giovinazzi and Leclerc. All three compounds are in use.

Vettel, who faces a grid penalty after taking on unspecified engine components, is among the early risers.

There's an early yellow flag when Alonso stops on track (Turn 12). Indeed, the session is red flagged.

It's clearly a technical issue as the Spaniard was told to "stop the car".

Onboard replay has the car sounding horrendous. There is fluid pouring from underneath the Alpine.

The all-clear is given with 49 minutes remaining, and Raikkonen - a winner here in 2018 - leads the way. In no time at all, all 19 drivers are on track.

Raikkonen posts a 39.888, but Ricciardo immediately responds with a 37.856. However, the McLaren driver's time is deleted for exceeding the track limits at Turn 9.

As Ocon and Gasly have their times deleted, Hamilton goes quickest with a 37.260. Bottas, like his teammate on softs, posts a 37.472, while Verstappen (softs) splits the Mercedes pair with a 37.337.

Perez goes fourth (37.624) on hards while Leclerc (37.790) is the quickest medium runner.

Again, Ricciardo has his time deleted, as does Stroll.

Out come the yellows when Leclerc goes off at Turn 6, the youngster losing the rear of the car in the Maggots/Becketts inspired complex.

Hamilton improves to 36.812 as Norris (softs) goes fourth (37.519).

Vettel (softs) goes fifth, ahead of Perez, Leclerc, Sainz and Ocon.

In addition to Turn 9, Turn 19 is seeing drivers penalised for exceeding the limits.

Norris complains of "front and rear locking".

Perez goes top (36.798) on the hards.

Meanwhile, Bottas will take a grid penalty after taking on a new ICE, just like his teammate did in Turkey. Russell will also take a hit after taking on a new ICE and other components.

Norris is unhappy with the balance of his car., though he is currently third quickest.

Hamilton improves to 36.831 as the majority of the field head back to the pits.

"A lot of overheating, on the rears particularly," reports Hamilton.

That new ICE for Bottas - his sixth of the season - is bad news for Mercedes and raises the question of whether Hamilton also faces another grid penalty.

On fresh softs, Vettel goes quickest (36.344), only to have his time deleted.

Switching to softs, Leclerc goes second (36.601), just 0.220s off Hamilton's pace.

"That's a god idea," responds Vettel, when advised to go for a double cool-down.

On fresh softs, Verstappen goes top (36.049), though he appeared to struggle with understeer, the Dutchman only posting a purple in the opening sector.

Mazepin is off at Turn 19 but is able to continue.

"Interesting pace," says Russell of Ocon's slow out lap, the Frenchman running the visor-cam today.

Quickest in all three sectors, Hamilton raises the bar with a 35.096, 0.953s quicker than his title rival.

Meanwhile, Alonso, despite his earlier issue, looks set to return to the fray.

Quickest in the final two sectors, Bottas posts a 34.874, 1.175s quicker than Verstappen.

"Too badly flat-spotted," I've got to box," says Norris.

To add to his woes, the Briton has his time deleted, as do Ricciardo (again) and Stroll (again).

Verstappen improves but remains 0.932s off Bottas' pace.

Meanwhile, a 36.674 sees Sainz go fifth, just behind his Ferrari teammate.

Alonso posts an exploratory 38.785 to go 18th.

With just over ten minutes remaining, attention is focussed on longer runs with high fuel.

Hamilton closes to within 0.045s of his teammate's best as Perez switches back to hards.

A 37.068 sees Alonso improve to 15th, around 0.2s off his teammate's pace.

Meanwhile, drivers continue to have time deleted, Perez and Mazepin among the latest.

While admitting that Mercedes advantage is down to "straight line speed", the Red Bull boss is confident that there is more to come from his own car.

"Brakes are all over the place," warns Russell.

As the clock ticks down, all bar Norris and Schumacher are on track.

As Raikkonen spins at Turn 9, the stewards are looking at an incident involving Perez and Schumacher which saw the pair clash after the German appeared to be letting the Red Bull pass only to turn in on it.

The session ends. Bottas is quickest, ahead of Hamilton, Verstappen, Leclerc, Sainz, Gasly, Perez, Norris, Giovinazzi and Raikkonen.

Russell is eleventh, ahead of Ocon, Stroll, Vettel, Alonso, Ricciardo, Latifi, Tsunoda, Schumacher and Mazepin.

Check out our Friday gallery from COTA, here.