Fernando Alonso, the only driver fighting Vettel for the title, was fifth.
Hamilton, in his last race with McLaren, had a lap of 1 minute, 14.131 seconds at Interlagos, edging Vettel's Red Bull. Vettel teammate Mark Webber was third in 1:14.198 and Jenson Button of McLaren was fourth in 1:14.217.
Alonso, who tested different wings during the morning session, clocked 1:14.392, finishing ahead of Ferrari teammate and home-crowd favourite Felipe Massa.
Vettel has a 13-point lead over Alonso and needs to finish fourth or better to become F1's youngest three-time champion at age 25. He can also be the first to win three in a row since Michael Schumacher in 2004.
There was just a second separating the top 11 drivers in the first session. Drivers from McLaren, Red Bull and Ferrari secured the top six spots.
Teams were given two sets of the prototype Pirelli tires that will be used next year, allowing them to have an idea of what to expect in their 2013 cars.
Drivers used the new tires during most of the morning session, with Hamilton complaining of overheating at times. Sauber's Sergio Perez — who will be replacing the British driver at McLaren in 2013 — said the new sets had more mid-corner grip.
Hamilton escaped a collision near the end of the practice after a Marussia car spun in front of him.
It was a hot and sunny day, but rain was expected for Saturday's qualifying and Sunday's race in Sao Paulo. The second practice is later in the afternoon.
Red Bull has won the last three races in Brazil and Vettel finished second last year at Interlagos. The German driver has finished fourth or better in the last six races this year, and two-time champion Alonso hasn't won since the German GP in July.
In addition to crowning the champion, the Brazilian GP marks the end to Schumacher's career for the second time. F1's most successful driver, Schumacher retired with Ferrari in 2006 and returned with Mercedes in 2010. He managed one podium finish this year.
Schumacher had the 11th fastest time in the first session on Friday.
It will be the sixth time since 2005 that the F1 season will be decided at the Brazilian GP. Alonso won both of his titles at Interlagos in 2005 and '06.
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