Ferrari F1 driver Fernando Alonso has named Lewis Hamilton and Sebastian Vettel as probably his toughest challengers for the 2012 title.With half of 2012's GP's done, Spaniard Alonso has won more than any other rival and has a 40-point lead in the Drivers' chase over Mark Webber but close behind are Webber's Red Bull team mate and 2011 champion Sebastian Vettel.Nipping at his heels is another 2012 race winner and former champion Lewis Hamilton.NINE RACES LEFTAlonso was quoted by Brazil's Totalrace as saying: "Hamilton and Vettel are the drivers we have focused on since the beginning. They are the biggest challengers, but all of the teams are close. I hope they will fight among themselves and not one will dominate."With nine races left in the 2012 season, Alonso is taking nothing for granted. "The distance between the top five, top six, is not impossible to recover," he said. "You just need one or two good races and you're up there."Pundits have lauded Alonso's extreme consistency so far in 2012; he's finished all 11 with points."Sometimes we know we can be on the podium," the 31-year-old said, "at other times maybe it's only seventh, but we cannot afford to make any mistakes or do anything that we will regret."Brazilian F1 veteran Rubens Barrichello told Germany's Auto Motor und Sport: "Alonso is in the form of his life. He doesn't have the fastest car but he's the one getting the best out of what he has and his rivals are taking points off one another."I see this (championship) as a duel between Alonso and Vettel."