Charles Leclerc led a Ferrari 1-2 in a frustrating final practice session for the Mexican Grand Prix marked by the track's changing conditions.
Leclerc led Vettel by a mere 0.027s, with the fastest times achieved in the dying minutes of FP3 as dry patches finally emerged around the track and allowed the filed to switch from intermediate to soft tyres.
Valtteri Bottas outpaced Mercedes teammate Lewis Hamilton for fourth while a solid effort from Carlos Sainz put the McLaren driver fifth, just ahead of Red Bull's Max Verstappen.
A poorly feeling Pierre Gasly did well to secure P7 ahead of Alex Albon, while Lando Norris and Sergio Perez rounded off the top ten.
Overnight showers left a damp track for drivers to deal with at the outset of the final practice session at the Autodromo Hermanos Rodriguez.
But the ambient humidity was the least of Pierre Gasly's worries, the Toro Rosso having to contend with a painful stomach bug that hit the Frenchman - and many other members of the F1 community - overnight.
As the session got underway, Gasly's seat remained empty, pending an update on the 23-year-old's condition.
Meanwhile, out on the track, Alex Albon, running on intermediates, was the first driver to put a proper time on the board, the Red Bull driver eager to put miles under his belt following his crash in FP2.
Albon was quickly overhauled however, first by Hamilton and then by Verstappen who shaved more than a second off his teammate's best.
It was all rather academic however with drivers - and a very limited number at that - running in a bid to dry the track rather then improve performance.
Racing Point's Sergio Perez also took to the track and gave the locals something to cheer about, but the tarmac remained only sporadically dry, keeping three-quarters of the field in the garage.
Speaking of garages, a glance at the Renault box showed both of the team's cars on their stands, their respective crews working diligently but with no drivers in sight.
The French outfit eventually revealed that a pollution of the cooling systems on both cars had required some careful cleaning. Both R.S.19s therefore remained confined to their garage in FP3.
Over at Ferrari, Sebastian Vettel also remained garage-bound, the Scuderia dealing with a sensor issue on the German's car.
Halfway through the session, Verstappen head the timesheet from Hamilton, Albon, Bottas, Magnussen, Grosjean, Raikkonen and Leclerc, the only drivers to have set a time at that point of FP3.
With 15 minutes left on the clock, a bold Raikkonen ventured out on a set of soft tyres, a move that prompted Mercedes to bolt on some mediums on to Bottas and hamilton's W10.
With dry patches now appearing more frequent, Raikkonen duly sprung to the top of timing screens with a 1m21.673s. But the Finn was quickly outpaced by Bottas and the Vettel as more runners switched to dry tyres.
As the times tumbled, traffic increased, and Albon went fastest with a 1m17.370s. Hamilton was seen running deep and over the grass at Turn 1 as grip remained at a premium.
The action was frantic in the final minutes of FP3 and permutations at the top were frequent.
Verstappen pipped Albon at the top of the boards but the Dutchman's reign was short-lived as McLaren's Carlos Sainz took charge.
With a minute the Spaniard was kicked off the top spot by Bottas who was closely followed by Hamilton as the Mercedes sat 1-2.
But the pair's Italian rivals were determined to have the final word, which they did as Leclerc and Vettel ultimately assumed control.
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