MEXICO CITY-- Red Bull's Daniel Ricciardo reminded Lewis Hamilton on Friday that he has a fight on his hands to win the Mexican Grand Prix however inevitable the Mercedes's driver's fourth world championship may be.
Hamilton is on the brink of becoming Britain's first four times world champion but he wants to do it with a victory on Sunday.
He is 66 points clear of Ferrari's Sebastian Vettel and needs only to finish fifth on Sunday to secure the title with two races to spare, even if the German wins.
The 32-year-old was the meat in a Red Bull sandwich in second practice at the Autodromo Hermanos Rodriguez on Friday, however, with Ricciardo top of the timesheets with a lap of one minute 17.801 seconds.
Hamilton had a big spin and was 0.131 slower with Red Bull's Max Verstappen third, 0.163 off his team mate's time, despite an engine failure with an older power unit that was of no concern.
Vettel was fourth, and also with a hot backside after his car's fire extinguisher went off beneath his seat half an hour into the session.
"On the long runs, I still think we could find a bit more," said Ricciardo.
"On low fuel we are more or less there. Mercedes always have more on Saturday so I think we still need to find a few tenths if we want to stay ahead of them.
"I feel we can be a bit better on race pace and I think we can improve a few things. I think these last three races will be pretty close between the top three teams."
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Finland's Valtteri Bottas had been fastest in the sunny morning session with a best lap of 1:17.824 also keeping Hamilton off the top. Verstappen and Ricciardo were third and fourth respectively.
Hamilton's 2016 pole position time was 1:18.704.
Red Bull and Ferrari had been expected to close the gap on Mercedes in the afternoon since they had used slower supersoft tyres in the morning while Mercedes set their best times on ultrasofts.
"I expect this weekend to be more fun than it has in the past," Hamilton had said on Thursday, with the 2017 generation cars significantly quicker on fatter tyres and changed aerodynamics to last year's on a low-downforce layout.
"I think Ferrari will be quick here. Their car should bode well here. I'm hoping we have a great battle," added the Briton.
Hamilton won at the high-altitude circuit last season and is the 1/500 odds on favourite to take the title.
Sergio Perez was seventh fastest for Force India before lunch, with regular team mate Esteban Ocon sitting out the session to make way for Mexican Adolfo Celis Jr. to give the home crowd two drivers on track.
Ocon will not have enjoyed being a spectator as Celis put the Frenchman's car backwards into the barriers at turn 16 and halted the session. Ocon returned to the cockpit after lunch and was 10th fastest.
New Zealander Brendon Hartley, preparing for his second race with Toro Rosso, managed only 10 laps in the morning with mechanics working on the car after he stopped on track.
He was 13th fastest in the afternoon
There were also more problems for McLaren, with Belgian Stoffel Vandoorne sidelined completely as the team changed his car's power unit to a spare. He already has a 35-place grid penalty.
