Alonso spoils Vettel's P3 moment.

Fernando Alonso completed a clean sweep of fastest times in practice for the United States Grand Prix ahead of qualifying for the race at Indianapolis, although he had to work hard to wrestle the best lap off Sebastian Vettel.

Once again getting more laps under his belt as he prepares for his qualifying and race debut, Vettel managed to pop in a time during that stint good enough to occupy the top of the timesheets up until the final minute and a half when Alonso spoiled his headline grabbing performance.

Nonetheless, it was a superb effort by Vettel, Alonso having to rely on a simulation qualifying run to emerge with the fastest time as he seeks his first pole position at the Indiana circuit.

Once again underlining McLaren's superiority, Lewis Hamilton was third quickest having led the way for the majority of the session before Vettel and Alonso arrived to push him back down.

Making it three rookies in the top four, Heikki Kovalainen made an unexpected appearance in fourth place as Renault came good when it mattered, his team-mate Giancarlo Fisichella also eighth fastest. Between them, Nick Heidfeld, Kimi Raikkonen and Felipe Massa in fifth, sixth and seventh were less of a surprise.

Just as they did in the first two practice sessions, David Coulthard and Nico Rosberg featured inside a top ten covered by less than a second, the Red Bull and Williams duo edging out the Toyotas of Jarno Trulli and Ralf Schumacher who showed better pace in 11th and 12th.

Anthony Davidson was 13th quickest, although having been unable to improve in the final seconds when the track conditions were improving, it suggests there could be more to come from the Brit in qualifying. His Aguri team-mate Takumsa Sato was 17th fastest.

Mark Webber was 14th in the second Red Bull, ahead of the leading Honda of Jenson Button in 15th, the Brit doing much better than 18th place Rubens Barrichello, who didn't set a time until half way through the session

Tonio Liuzzi was the best of the Toro Rossos in 16th, with Scott Speed 20th, the American a spot behind the second Williams of Alex Wurz. Spyker meanwhile once again brought up the rear in 21st and 22nd, Adrian Sutil ahead of Christijan Albers but both the only drivers outside of the 1min 14secs range.