A sensational double eagle finish from Rory McIlroy gave him a six-stroke cushion going into the final round of the British Open as he crushed a chasing pack of challengers who tried and failed to hunt him down during a rain-hit third round.

The 25-year-old Irishman, looking to add a third major to his collection and a first on British soil, started Saturday with a four-stroke lead.

But by the time he reached the 12th hole that had vanished and he was caught in a dogfight with American shot-maker Rickie Fowler, hungry to win his first major.

That was when McIlroy, who had been struggling off the tee, produced his best golf of the week at Royal Liverpool.

A birdie at 14 eased him back ahead, and with Fowler going off the boil, McIlroy struck what could prove to be two tournament-winning blows with magnificent eagles at the 16th and 18th.

That put him at 16-under for the tournament six strokes clear of Fowler who had eight birdies en route to a 68.

It was the biggest lead at the third-round stage of the Open since Tiger Woods at St Andrews in 2000. Woods eventually won by eight strokes on that occasion.

A further stroke back came Spaniard Sergio Garcia who had a 69 and Dustin Johnson of the United States with a 71. Frenchman Victor Dubuisson was next best on eight under after a 68.

It was already a remarkable day for the British Open because for the first time in its 154-year long history the field went out from both the first and 10th tees instead of just everyone going off the first.

That was due to a decision taken by tournament organisers the R&A to bring forward the start times and share them between 1 and 10 in an effort to complete the round in the face of bad weather forecast for later on.

As it was, the 72-strong field was greeted with torrential rain as they arrived at the historic links layout on the Wirral peninsula south of Liverpool.

McIlroy was the man to catch and when he bogeyed the first hole, the chase was immediately on.

Johnson, Garcia, Jim Furyk and Charl Schwartzel all made early surges, but McIlroy struck a timely birdie on the fifth and then a series of fine approaches and clutch putting allowed him to keep his nose in front.

Then Fowler emerged from the chasing pack with three straight birdies from the 10th. When McIlroy dropped a stroke at the 12th, the solo lead he had enjoyed from the first day had gone.

But with the rest of the pack scenting blood, McIlroy suddenly put his foot on the accelerator with his two eagles, leaving his stunned rivals in his wake.

Catching him on Sunday will be a momentous task for any player as the Irishman seeks to add the British Open to the US Open crown he won in 2011 and the PGA Championship title of 2012, both by eight strokes.

Phil Mickelson saw his chances of defending the title he won last year at Muirfield vanish as he shot a 71 to stand at one under for the tournament, while world number three Justin Rose ended the day at five under after a 69.

World number one Adam Scott had a fine 69, but at six under is too far back to pose a serious threat.

Woods, meanwhile, had another mixed day as he carded a 73 to stand at three over, 17 strokes off the lead.