Fernando Alonso said he needed a new challenge when he left Renault last year and the double world champion has found it several times over in McLaren team mate Lewis Hamilton.

Hamilton, the 22-year-old Briton who has taken Formula One by storm in his rookie season, collected his second win in a row at Sunday's U.S. Grand Prix in Indianapolis to go 10 points clear of the Spaniard after seven races.

British bookmakers have him as favourite to win the championship.

This was not the script the Spaniard envisaged when he arrived at McLaren as the knight in shining armour, the man to take on Ferrari and Renault and lead them back to the top after a barren year.

"I think it has been a surprise for me and a surprise for everybody, to see him doing so well," Alonso said after finishing second on Sunday.

"But you know, I have big confidence. We have only done seven races, 10 to go."

Alonso, who only last month said he was more worried by Ferrari's pace than by Hamilton, will need to call on all his reserves because the rookie is now the biggest obstacle to his hopes of back-to-back titles with different teams.

PRIVATE DUEL

Indianapolis served up a real tussle between the team mates with Alonso and Hamilton dicing at the start and then running wheel to wheel down the straight midway through the race at around 300kph.

Ferrari's Brazilian Felipe Massa, third overall, is now 19 points off the lead while team mate Kimi Raikkonen is fourth and 26 behind Hamilton -- requiring a comeback of epic proportions for the Finn to take the title.

A private duel is emerging, one in which McLaren treat both their drivers as equals while doing their best to prevent open warfare from breaking out.

Alonso has never been in this situation before with a team mate and the strains are plain to see, with the Spaniard showing evident frustration in Sunday's race in Hamilton's slipstream.

Whatever happens in the next round in France on July 1, Hamilton will start his home British Grand Prix a week later on top of the championship on points at least and as clear favourite for Silverstone.

The Briton is beating the Spaniard at his own game, a model of consistency who has been on the podium in every race.

Hamilton won in both Montreal and Indianapolis, despite never having raced there before, and is completely familiar with the European tracks ahead.

His confidence is growing by the day.