Max Verstappen topped the timesheets in FP1, however, with drivers running 2020 prototype compounds in addition to the current tyres it was hard to get a real idea of the true pecking order.
That said, it's a promising start for the Dutchman and Red Bull.
Both Mercedes drivers spent much of the session on the 2020 rubber, and while Lewis Hamilton made a late improvement to fourth on the 2019 tyres, he was one of a number of drivers to have their times deleted after falling foul of the track limits sensor at Turn 19.
Indeed, Verstappen had his times deleted twice, and while that isn't really important at this stage of the weekend, it could become an issue come qualifying.
Vettel was second quickest, ahead of Albon, Gasly, Ricciardo and Grosjean, on a morning that temperatures dipped below those usually encountered during pre-season testing.
One bone of contention for the drivers, other than the track limits sensor, was the bumps, which appear to be worse than ever. Hamilton, expressing concern that they constitute a danger, adding that they are the worst he's even encountered.
Fact is, they're there and they are the same for everyone, so the drivers just have to accept it.
A number of drivers had issues earlier, not least Nicholas Latifi who only managed 7 laps as a result of a gearbox issue, while Leclerc (throttle), Hulkenberg (hydraulics) and Sainz (floor change) also lost track time.
It's believed Leclerc's throttle issue could have been caused by the bumps.
Ahead of the start of the session, the air temperature is 15.4 degrees C, while the track temperature is 24.4 degrees. It's almost balmy compared to earlier.
The lights go green, and Kubica is first out, followed by Albon. The pole is running the 2020 tyres, while the Thai is on mediums. Russell, who handed his car over to Latifi earlier, is also on the 2020 rubber.
Albon posts 26.949 and Russell 42.507 as Kubica pits.
"Tyres already look better than FP1," Norris is told.
"It's more windy," reports Magnussen, who is told there is a head wind on the long back straight leading to Turn 12.
A 36.395 sees Hamilton goes quickest, ahead of Kvyat, Sainz and Albon.
As the Mercedes pair head out, Albon re-takes the top spot with a 35.411.
Bottas posts 35.108 as Leclerc goes quickest in S1. The Ferrari driver subsequently goes top with a 34.742.
Oh dear. It's game over for Grosjean who is off and on the grass at Turn 5. Replay shows him losing the rear of the car following a snap of oversteer and hitting the barriers, damaging the front wing and suspension.
Unfortunately for Haas, the Frenchman was running the new front wing, while teammate Magnussen was running the old version. It's unclear if the American team has a spare.
"I'm OK, but the car is not," he sighs.
The session is red flagged as the car is removed from the side of the track.
The session resumes after a couple of minutes, and within seconds there are a number of drivers back on track, among them is Hamilton, who is running the hards.
While Hamilton is on hards, his Mercedes teammate is on mediums, the team clearly splitting strategies, as is Ferrari, which has Vettel on hards and Leclerc on mediums.
"No bite from the brakes," reports Russell.
Hamilton goes third with a 35.103, behind Leclerc (34.434) and Verstappen (34.710), as Grosjean arrives back in the paddock... on foot.
Bottas is fourth, on a softer tyre than his teammate, ahead of Kvyat, Albon and Grosjean.
Told he can do another push lap, Ricciardo admits; "I don't think it will go quicker". Like his teammate he is on the 2020 rubber.
A spin for Giovinazzi in Turn 6 briefly brings out the yellows.
A 34.592 sees Hamilton improve to second, just 0.158s off Leclerc's best. The Monegasque on mediums and the Briton on hards.
"Drivability is poor out of Turn 11," reports Kvyat.
"Can I have these front tyres re-balanced, please," asks Hamilton.
"The tyres are really dropping off," says Verstappen on his 11-lap old mediums.
Albon is also suffering on his 12-lap old prototypes.
With 50 minutes remaining, Racing Point reveals that it has concluded its prototype running.
Magnussen is the first switch to softs, the Dane subsequently going eighth with a 35.442.
More drivers switch to the red-banded rubber, among them are Bottas and Vettel.
While the Finn posts a PB in S1, the German goes quickest. Again, Bottas posts a PB in S2, while Vettel goes quicker still. At the line Bottas posts 34.697 to go quickest, but this is immediately beaten by his Ferrari rival who stops the clock at 33.890.
Leclerc (softs) goes quickest in S1, but loses ground in the second sector. Nonetheless, a strong final sector sees him go top by 0.357.
All eyes on Hamilton who begins his qualifying sim. A PB in S1 is followed by a purple in S2. At the line the Briton posts 33.232 to go quickest, albeit courtesy of a tow from Kubica's Williams in the second sector.
"That's a good lap," says Gasly as he goes fifth with a 34.509. Indeed, it was a very good lap.
The qualifying sims out of the way, the majority of drivers switch focus the to the opening stint on Sunday.
Meanwhile, Bottas queries where Hamilton got his S2 time from. As the Finn is told about the tow from Kubica, it is likely that other teams will have noticed this as well and are adopting their strategy accordingly.
Verstappen goes third with a 33.547, as Sainz improves to seventh (34.667).
Posting a PB in S1, Albon subsequently has two poor sectors but still manages to go sixth (34.434), while Norris improves to 11th with a 34.882.
"It's getting colder out here," reports Hamilton.
"Did you hear that?" asks Russell. "Very dodgy noise from the gearbox when I launched." Of course, his car, albeit in Latifi's hands, had a gearbox issue in FP1.
On the race sims, in quick succession Hamilton and Vettel have laps times deleted for running wide in Turn 19. The Briton is appraised of the fact that two of his laps have had their times deleted.
"What the **** is Perez doing," asks Russell.
A strange spin in Turn 13 for Vettel. The replay suggesting some sort of power surge halfway through the corner.
Told Hamilton's lap time is 39.7, Leclerc responds: "No way, I can't do that!"
Talking of Hamilton, the Briton switches to the hard tyre.
"The front is weak," reports Bottas, "the front-left, I can see some graining."
Check out our Friday gallery from Austin, here.
"Try to upshift before the bump at the exit to Turn 9," Leclerc is told.
As Vettel switches to hards, Leclerc and Verstappen are on mediums, while Bottas is on softs.
"I feel the deg, so I'm having to work a bit harder for it," reports Ricciardo.
Told again to upshift before Turn 9, Leclerc says he is already doing it, that he's upshifting before the bump, and on board coverage appears to confirm that he is.
Woah! Stroll almost runs into the rear of Sainz' McLaren, as the Spaniard goes very wide and then cuts across the front of the Racing Point, seemingly unaware it was there.
The session ends. Hamilton is quickest, ahead of Leclerc, Verstappen, Vettel, Bottas, Albon, Gasly, Sainz, Stroll and Giovinazzi.
Ricciardo is eleventh, ahead of Kvyat, Hulkenberg, Norris, Perez, Raikkonen, Magnussen, Grosjean, Russell and Kubica.
Check out our Friday gallery from Austin, here.