World number five Dustin Johnson led a strong American challenge behind early clubhouse leader Jarrod Lyle in the opening round of the $1.54 million Australian Open at The Lakes on Thursday. Johnson, here for next week\'s President\'s Cup as the top-ranked American player, fired eight birdies in his six-under 66 to trail Australian Lyle by a shot with half the field still on the course. Lyle, who finished only once in the top 10 on this year\'s US PGA Tour, carded a seven-under 65 in an unblemished round that included an eagle three at the 14th and five birdies. Former world number one Tiger Woods and leading Australians Jason Day and Adam Scott were playing in the afternoon groups. Johnson, who had a win and six top-10 finishes on the US PGA Tour this year, said he was a \"little rusty\" early after six weeks without a tournament. \"I made a lot of good putts, some tap-ins and some three-four footers, and I played really solid all day and made some great iron shots,\" Johnson said. \"I was a little rusty at the start, it was the first time I\'ve been in competition for five-six weeks now, but then got it going pretty well.\" Johnson said a round of seven or eight under was definitely achievable with all the par-fives on the course reachable and a lot of the par-fours not too challenging. Lyle, who fought off leukemia at the age of 17 in 1999, said it was his lowest score in what had been a rough year on the US PGA Tour where he finished 161st and is heading back to the secondary Nationwide Tour next year. \"That\'s the lowest score I\'ve shot all year, I\'ve played solid all year, but just haven\'t achieved anything,\" Lyle said. \"On the course it\'s been a really rough year and off the course it\'s been awesome (engaged and expecting his first child).\" Former US Masters champion Fred Couples, who will be the non-playing captain of the US team at next week\'s President\'s Cup teams event against the Internationals at Royal Melbourne, opened up with a five-under 67, two shots off the lead. Couples, 52, who has 53 tournament victories in his 30 years as a professional, carded six birdies and a bogey playing with American John Cook and veteran Australian Peter Senior. World No.17 Bubba Watson, another member of next week\'s US team, chimed in with a four-under 68 with an eagle, five birdies and three bogeys.