Max Verstappen has posed Lewis Hamilton his toughest challenge EVER, claims Christian Horner, as Red Bull chief insists world championship triumph for Dutchman would be his team's 'biggest achievement'

• Max Verstappen has posed Lewis Hamilton his toughest challenge this season 
• Christian Horner claims no other driver has gone toe-to-toe with the Briton 
• The Dutchman, 24, leads the championship by six points heading to Texas
• Horner says victory for his man would be Red Bull's 'biggest achievement' 

Christian Horner believes that Max Verstappen has provided Lewis Hamilton his most difficult challenge to date, as the Red Bull chief insisted world title triumph for his man would be the team's 'biggest achievement'.

Verstappen, 24, and Hamilton, 36, have gone toe-to-toe over the course of 16 races this season, with the Dutchman leading the championship race by six points heading into this weekend's US Grand Prix.

Hamilton is looking to clinch a record-breaking eighth world championship this term, but has faced a stern test from his rival, whose Red Bull has been superior for much of the campaign.

And Red Bull chief Horner has claimed that the challenge posed by Verstappen is something Hamilton has rarely had to contend with during his illustrious career, adding that there is a lot at stake for the Mercedes man.   

'I think, inevitably, there's always going to be an evolution,' the Red Bull team principal told The Guardian.

'Lewis has had an amazing career and he's still in fantastic form. He's still a titan of the sport. The fact that Max is able to go toe-to-toe with him is probably something Lewis hasn't had throughout his career – certainly through the championship years. There's nothing with this degree of intensity.

'There's obviously a lot at stake for him as he's going for a record-breaking eighth championship, Max is going for his first and he knows he's got many more years to come.'

Should Verstappen triumph this season, it will be the team's fifth world championship, with former star Sebastian Vettel winning four titles between 2010 and 2013.

However, winning in the hybrid era - where Mercedes have been ruthlessly dominant - would make this victory his team's most impressive to date.

'It will be our biggest achievement,' Horner added.

'If you look at the strength of Mercedes, and the dominance they've had, it's clear that nobody's come near them for years. No one has put them under this kind of pressure at this stage of the season.

'So it will be an enormous achievement if we pull it off.'