Martin Kaymer has insisted that he can't afford to take his foot off the gas as he looks to win his second Major tournament at Pinehurst this weekend.

The German recorded a second round of 65 to lead the US Open by six shots at the halfway stage in North Carolina, but he is fully aware that the picture can quickly change at the top of the leaderboard.

"It's not a done deal," the 29-year-old told members of the media. "You don't approach Saturday and Sunday in a relaxed way.

"There's never a time where you can relax. Unless it's Sunday afternoon and you're raising the trophy, then you can relax. Until then, you've got to keep playing."

Kaymer recorded his only success in the Majors at the 2010 USPGA Championship.