Jenson Button: Fernando Alonso tougher to beat than Lewis Hamilton

Button raced alongside countryman Hamilton in the 2010-12 seasons, before the now three-time F1 world champion left for Mercedes, while Alonso joined McLaren from Ferrari this year.

During their three seasons as team-mates, Hamilton twice finished fourth in the drivers' championship to Button's fifth, while Button was second and Hamilton fifth in 2011.

While they have generally been fighting at the back this year, Button says Alonso has been a tougher opponent.

"In a race, it's a bigger challenge, I would say, a more consistent challenge," Button said.

"He's always there. On some race days, Lewis was untouchable. And on other race days, it was like, 'where is he?'

"I'm guessing he's a different driver now, more experienced, but Fernando is always there, always competitive.

"If he's in front of you, you're holding on, and if he's behind you, he's pushing you a lot.

"That's great, though, I like that. I think that's important in a team.

"It's definitely helped us this year."

Button dismissed Alonso's self-criticism aired earlier this month - when the Spaniard argued he had not been driving well this year - as "clever drivers say clever things".

He is, though, happy with his own performances, amid the challenge of "trying to hold onto the back of the field", citing being able to mix it with faster cars during the mixed-weather United States Grand Prix as a highlight.

"If you're fighting people it's not such an issue," he said of the McLaren-Honda's shortcomings.

"In Austin, we were able to fight people and it's not near the front - sixth is not too bad - but still we could race people and if that was for 14th it still would have been fun, because at least you're still racing people.

"You've got to keep your nose clean, which is a big part of it for us at the moment."