BETHESDA (AFP) - Relentless Rory McIlroy showed no mercy to his pursuers in the US Open third round on Saturday as he extended his lead at Congressional Country Club to an astonishing eight strokes. Bristling with confidence, the Ulsterman fired a 68 for a US Open record total of 14-under par and he ended the day comfortably clear of South Korea's Yang Yong-Eun, who was alone in second after a 70. England's Lee Westwood and Jason Day of Australia, who both had 65s, and Robert Garrigus of the United States, with a 68, were a further stroke back. McIlroy's eight-stroke lead is the largest at the US Open after 54 holes since Tiger Woods led by 10 at that stage at Pebble Beach in 2000. Woods eventually won by a majors-record 15 strokes. The Irishman also led the Masters after three rounds in April, by four strokes, before ending up in a tie for 15th after a closing 80. This time, though, the gap at the top of the leaderboard is enormous for a major tournament and it would take an unprecedented collapse for McIlroy to be deprived of his first major title at the tender age of 22. "What I did today, I tried to set myself a little target, little goals, just because it kept me from focusing on the leaderboard and focusing on how far ahead I was or anything like that," he said. "So just giving yourself little goals throughout the round, that really kept me in the present and kept me focused on my game." Playing with Yang, McIlroy started the day with a six-stroke margin, the equal-best-ever halfway lead in US Open history. He parred the first three holes and then a birdie at the fifth, coupled with a bogey from Yang on the second, when he failed to get up and down from a greenside bunker, meant that McIlroy had extended his lead over the Korean to seven. The Irishman then narrowly missed a long putt for eagle at the ninth, but the ensuing birdie tap-in left him two-under for the day and 13-under for the tournament, eight ahead of the field. The Ulsterman had blown the field apart in the first two days with rounds of 65 and 66 giving him the lowest first 36 holes in US Open history. He had stood at 11-under, six clear of second-placed Yang with a group of five players a further three strokes adrift. McIlroy dropped just his second stroke of the tournament when he failed to get up and down from a bunker at the tricky par-three 10th. But it was back to business as usual at the next hole, the hardest on the course, which he birdied with a 12-footer and celebrated with a delighted punch of his fist. His golf was of the tallest order and a six-footer for birdie at the 14th made him the first golfer in US Open history to get to 14-under par. He stayed there to the end of the round, missing a 10-footer at the last which would have got him to 15 under. Yang dug in and birdies at 14 and 16 kept him in second and ensured him another outing in the company of McIlroy on Sunday. "I wanted to catch up a little bit, but at the same time, the player with the better shot, with the better putt, with the better composure is leading right now. So I have no regrets," was his blunt assessment of his position. Westwood, a Ryder Cup partner of McIlroy, began the day seemingly out of it at one-over and he did little of note down the front nine. But three birdies and an eagle in a four-hole stretch from the 13th suddenly saw him leap into second place as he came in with a tournament equal-best of 65. "You don't know how Rory is going to do. You don't know how he's going to deal with the big lead," said Westwood optimistically. "He had a big lead in a major and didn't deal with it well before. There's pressure on him with regards to that." On another hot, humid day outside Washington, Day also got to five under after another spectacular round of 65, which included birdies in three of the last four holes. "The more times I put myself in this position, the better chance I have of winning a tournament," said 23-year-old Day, who finished in a tie for second at the Masters in April. "I'm very excited to be where I am right now. I'm just looking forward to tomorrow. Obviously it's going to be pretty tough to see if we can try and catch Rory." Defending champion Graeme McDowell came in with a 69 which left him at level par for the tournament. World No.1 Luke Donald, though, had another frustrating day and the Englishman walked off with a three-over 74 for seven-over for the tournament, 21 strokes off the lead. What remains to be seen now is whether McIlroy can avoid the kind of collapse that hit him at the Masters. This time with an eight-stroke advantage the chances of that happening look highly unlikely as he closes in on succeeding fellow Ulsterman Graeme McDowell as US Open champion.