The US Grand Prix in Austin looks set to offer a tantalising battle between championship rivals Lewis Hamilton and Nico Rosberg this weekend after the Mercedes team-mates were split by just 0.003s in Friday practice. With just three rounds of the championship remaining and 17 points separating Hamilton and Rosberg, the Circuit of the Americas will play host to a crucial chapter in the 2014 title battle. Hamilton, who is hunting his second world title, got the edge on the first day of running by beating Rosberg in the timesheets, but had his final session cut short when his car was stripped down in the garage after just 18 laps of the second session. That means Hamilton missed out on important race preparation and will be chasing his set-up ahead of Saturday's qualifying. Meanwhile, Rosberg had a trouble-free session and with a tiny gap separating the two drivers around the 5.5km circuits he is within striking distance of Hamilton. The same cannot be said of the rest of the field, with Ferrari's Fernando Alonso 1.104s off Hamilton in third and Red Bull's Daniel Ricciardo 1.305s off in fourth. Williams was Mercedes' closest rivals at the last race in Russia, but Felipe Massa could only manage the fifth fastest time ahead of Kimi Raikkonen. Daniil Kvyat's impressive form in the Toro Rosso continued with the seventh fastest time ahead of the McLarens of Kevin Magnussen and Jenson Button, which appeared to drop off the pace after a strong showing in the morning session. Valtteri Bottas was outside the top ten, but will likely recover tomorrow as Williams often holds back its true potential during Friday practice. World champion Sebastian Vettel finished the session rooted to the bottom of the timesheets as he bedded in a new power unit for this weekend. According to the regulations, his change in engine, turbo and energy recovery system means he will be forced to start from the pit lane on Sunday, so his 16 laps – and slower lap times – were focused on race set-up rather than chasing a quick time for qualifying.