BETHESDA (AFP) - Rory McIlroy's history-making start to the 111th US Open became official Saturday morning with the completion of the storm-interrupted second round at Congressional Country Club. The 22-year-old Northern Ireland prodigy fired a five-under par 66 on Friday to seize a six-stroke lead over South Korean Yang Yong-Eun, McIlroy's total of 11-under par 131 the lowest 36-hole start in US Open history. "I've played two really good rounds of golf but I know I have to play another two really good rounds of golf if I want to win," McIlroy said. "I have to keep it going over the next couple of days. I'm halfway there, but there is still a long way to go." A storm that halted play Friday for 42 minutes pushed the conclusion of the second round to Saturday morning, but none of the 21 players who had to return to finish were a threat to approach McIlroy or even Yang. In all, 72 players made the cut at four-over par 146. McIlroy is the youngest 36-hole leader at the US Open in 97 years, since Walter Hagen led the 1914 US Open at age 21. The Ulsterman's margin matched the largest 36-hole lead in the tournament's history, the six-stroke edge Tiger Woods enjoyed after two rounds at Pebble Beach in 2000 on his way to a majors-record 15-stroke romp. That victory began a run of four major triumphs in a row for Woods, the infamous "Tiger Slam". And with McIlroy contending in his fourth major in a row there are many who already see the rising star as the next Tiger. But such comparisons might wait until McIlroy wins a major title. He has squandered two great chances with big leads in prior majors and learned from the experiences. At the Masters two months ago, McIlroy led by four shots entering the final round and by a stroke with nine holes to play before a triple-bogey at the 10th led to a horrid back nine and a final round 80 that left him sharing 15th. Before that, he matched the lowest round in major golf history with a 63 to start last year's British Open at St. Andrews only to run afoul of swirling winds that soared his score to a second-round 80. McIlroy became the first player in US Open history to reach 13-under par at any point in any US Open when he birdied the 16th and 17th holes, surpassing the old low of 12-under set by Gil Morgan in 1992 and matched by Woods in 2000. And McIlroy did it in only 35 holes. But he received a wake-up call with a double-bogey on the 18th to end his second round when he was on the verge of the lowest first 36 holes in major golf history.