Jason Day has rebounded in style from his vertigo attack to be in major championship contention yet again after his first round of the British Open at St Andrews.

In his first outing since his heroic top-10 finish at last month’s US Open, Day carded an unblemished six-under-par to trail early clubhouse leader Dustin Johnson by a shot.

On medication and showing no sign of any ill-health, the world No.9 accrued six birdies in a flying start to his quest for an overdue major title.

Day is one stroke ahead of fellow Australian Matt Jones after the pair capitalised on ideal morning conditions at the Old Course on Thursday.

Three-times a runner-up at golf’s biggest events, Day’s birdies came on the second, fifth, sixth, 10th, 14th and 15th holes.

He could have picked up one or two more shots with a touch of luck and had his putter run a little hotter.

Day almost holed out for eagle on the 15th before narrowly missing out on a chip-in birdie at St Andrews’ treacherous 17th Road Hole.

Day’s back-nine charge overshadowed a fine round too from Jones, who helped himself to five birdies in the 35-year-old’s first competitive look at the home of golf.

“It’s great to get off to a start like that playing my second British Open, especially playing this golf course,” Jones said.

“I played smart out there, just kept it out of trouble and gave myself some birdie chances and made a nice one on the last there.”

While Day and Jones are well in the mix, veteran Rod Pampling faces a mammoth battle to make the halfway cut after opening with a five-over-par 77.

After getting to one under with a nice birdie on the par-3 11th, Pampling’s round began to slip away when he took a double-bogey on the 14th.

A first-round leader of the Open back in 1999 at Carnoustie, Pampling then bogeyed his last four holes to fall a dozen strokes adrift of the early tournament leaders.

“I just didn’t make a one-putt today,” Pampling lamented.

“For whatever reason, I just didn’t have anything going on the greens.”