Ferrari's Sebastian Vettel topped the second practice session for the Mexican Grand Prix on Friday afternoon, posting a blistering 1m19.790s on the supersoft tyre, to head Mercedes' Lewis Hamilton by the smallest of margins at just 0.004s.
The pair had a four-tenth margin to those behind, with championship leader Nico Rosberg third, 0.0435s adrift of Vettel's best time, narrowly ahead of fourth-placed Kimi Raikkonen.
Mercedes looked to struggle on the softest compound, but looked strong during their longer runs on the soft and medium tyre, whilst Ferrari were somewhat the opposite with strong single lap pace.
Red Bull's Daniel Ricciardo was fifth, with the Force India of Nico Hulkenberg splitting the two Red Bulls as Max Verstappen the seventh quickest time, eight-tenths back on the best of the session.
Valtteri Bottas, Carlos Sainz and Fernando Alonso completed the top ten.
Haas endured a tough session as Esteban Gutierrez finished practice slowest, while team-mate Romain Grosjean missed most of the session due to a hybrid system fault.
