For the second time this weekend it was Red Bull's Max Verstappen who led a session in Austin as he set a flying lap of 1m 33.305s to keep Ferrari’s Sebastian Vettel at bay by 0.218s – with McLaren’s Lando Norris half a second back in third place.
Verstappen set the fastest times in sectors one and three to eclipse Vettel as the two traded positions at the top of the standings as soon as qualifying simulations on soft tyres began halfway through the hour-long session.
Vettel ended up the only Ferrari driver to set a laptime as his teammate Charles Leclerc seemed to lose power towards the end of the lap and pulled over on the run-off before the penultimate corner.
Problems for Leclerc
Ferrari revealed after the session that an oil leak had caused the stoppage and said it would revert to an older engine for the remainder of the weekend, thus avoiding a grid penalty.
Light smoke was emerging from the rear of his Ferrari as he came to a rest and continued to do so as the car was wheeled behind the barriers.
The recovery of Leclerc's car, which was eventually returned to the Ferrari garage mid-way through the session, caused a brief virtual safety car period before the session resumed under green flag conditions.
McLaren’s Norris emerged first when the lights went green at the start of the hour and secured an impressive third in the final order, leaving Mercedes' Valtteri Bottas to settle for fourth, six-tenths off the leader’s pace.
Red Bull’s Alex Albon couldn’t match his team mate, finishing behind Lewis Hamilton in P6.
Mercedes have the race pace
Despite finishing the session in both P4 and P6, Mercedes’ long run times seem to suggest that they are the team to beat on Sunday, although Hamilton is wary of the fight Red Bull and Ferrari may bring.
Hamilton was unable to construct a qualifying run together but sector times from both him and Bottas suggested they will be near the front later this afternoon.
Carlos Sainz was twice as far from the benchmark in seventh as his teammate Norris, but shunned the soft tyre for most of the session.
He was 1.1s off the pace, but a tenth quicker than the Alfa Romeo of Kimi Raikkonen in eighth.
Pierre Gasly continued his fine weekend form and put his Toro Rosso into P9 and Daniel Ricciardo's Renault completed the top 10.
At the back of the field, without a representative time in 19th, Sergio Perez's Racing Point was fitted with a new engine, turbocharger, MGU-H and MGU-K for final practice.