Lewis Hamilton considers Sebastian Vettel to be a serious threat to his championship bid, but has hailed Ferrari's resurgence as "great" for Formula One.
Hamilton remains the odds-on favourite to secure consecutive titles despite Vettel's victory in Singapore last Sunday.
With six races to go, the Ferrari driver is now 49 points adrift of Hamilton, who retired for the first time this season after a loss of power at the Marina Bay Street Circuit.
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It marked Vettel's third victory of an impressive debut season with Ferrari after triumphs at the second race of the season in Malaysia and then in Hungary.
"How serious I take this challenge has not changed since Malaysia," Hamilton said. "For me, everyone is a threat and they have been since Malaysia. They won there so since then we have always kept them in view.
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"When we got to Monza they took another step, so nothing has really changed for us. It is great for the sport."
Mercedes to bounce back
Hamilton's Mercedes team, who have dominated the sport for two years, were mysteriously off the pace in Singapore.
They attributed their lacklustre display to their tyres at a track that they claim simply did not suit their package.
And Hamilton has backed Mercedes to bounce back in Japan this weekend despite suggestions to the contrary in the immediate aftermath of Sunday's race.
"The team has come up with a lot of solutions, a lot of reasons, for it being the way it was." Hamilton, who was an astonishing 1.5 seconds adrift of Vettel in qualifying in Singapore before retiring from the race after a part broke on his engine.
"The majority of them believe at least one of the many solutions or reasons they have come up with had a domino effect, so I am confident it has been understood.
"You can never say never, so I am not sitting here thinking it was a fluke. Sometimes there are going to be situations like that, but I am hoping that we have learned from that weekend and it won't happen again. It was specific for Singapore so it should go back to normal this weekend."
Hamilton is 41 points clear of team-mate Nico Rosberg, who crossed the line in fourth on Sunday, with Vettel eight points further back.
"He is a threat and we are keeping an eye on him and Ferrari in general because they have been very strong at times this year," said Rosberg.
"They are our closest competitors and they are capable of any thing - we need to be careful.
"But championship-wise I am not looking backwards, I am just looking forward, because if it comes to that, then third or second is not really a difference for me.
"I am going for first place this year - I have already been second - so I am only looking forward.
"Sebastian being a couple of points closer does not make any difference to me. I am just looking at the 41 points to Lewis."
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