Charles Leclerc headed Sebastian Vettel as Ferrari left it late to usurp an improved Mercedes in the closing stages of a wet-dry Practice Three session ahead of the Mexican GP.
The condition of the circuit - damp and slippery for most of the hour after heavy overnight rain, before rapidly drying - made the timesheet a little more inconclusive than normal heading into qualifying, which begins at 7pm BST.
But Mercedes ended up much closer to favourites Ferrari than was the case on Friday, with Valtteri Bottas just 0.114s back on the red cars in third.
Lewis Hamilton was fourth in the second Mercedes, with McLaren's Carlos Sainz up in fifth ahead of Red Bull's Max Verstappen. But the Dutchman did not improve to the extent of others after being held up on his final attempt.
Vettel, Friday's pacesetter, finished just 0.027s back on Leclerc's 1:16.145 time after dropping time in the last sector of his final attempt.
"I think Sebastian has a lot more in his locker," said Sky F1's Jenson Button. "I don't think he wanted to show his hand. I think we're going to see Ferrari extend their margin to Mercedes in qualifying."
Despite feeling unwell on Saturday morning and missing the first half of the session, Pierre Gasly impressed again to take seventh place for Toro Rosso. Alex Albon, returning to the track after his crash in P2, briefly lead the timesheet in the earlier stages of running, before being shuffled back to eighth after setting his best slick times earlier.
Lando Norris for McLaren and local favourite Sergio Perez for Racing Point rounded out the top 10.
But P3 proved a write-off for Renault, who lost both their cars from running due to issues related to their cooling systems on the RS19.
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