Thailand's Thongchai Jaidee had three birdies in the last six holes for a six-under par 66 and a one stroke lead at the halfway stage of the $2.5-million Dubai Desert Classic Friday. The 40-year-old former paratrooper continued the rich vein of form he showed last year when he won the Asian Tour Order of Merit title for an unprecedented third time to get to eight under for the tournament. That was one clear of a trio comprising European No.1 Lee Westwood, who had a tournament best 65, Spanish veteran Miguel Angel Jimenez, who had a 67, and Welsh journeyman Stephen Dodd, who had a 69. Defending champion Rory McIlroy of Northern Ireland was on six under after a 70, tied with big-hitting Spaniard Alvaro Quiros (69), Marcus Fraser of Australia (68), Edoardo Molinari of Italy (70) and Charl Schwartzel of South Africa (70). Thongchai's bogey-free round saw him reach the turn in three-under 32, before he produced his grandstand finish over the home stretch. He put his improvement in form over the last year down to a strict fitness regime that has seen him overcome severe back problems that laid him low two years ago and to his improved putting. It was a consumate performance from the 36-year-old Westwood, who clinched the inaugural Race To Dubai title last November by winning the season-finale at the nearby Earth Course. Like Thongchai his card was bogey free with three birdies on the front nine and four on the back nine. His showing was all the more encouraging in that Westwood is a self-styled slow starter to the season. There was a fine performance also from US golf great Tom Watson who was making his debut in Dubai at the ripe old age of 60. Last year's British Open runner-up shot a fine two-under 70 and at one under for the tournament comfortably made the cut. Fellow American veteran Mark O'Meara, who won here in 2004, was on his way home, however, after a 75 that left him eight over for the tournament. Johnson grabs lead In California, American Dustin Johnson putted masterfully to card a bogey-free seven-under 64 and take a one-shot lead after the first round of the Northern Trust Open Thursday. Johnson shot 32 on both the front and back nines on the par-71 Riviera Country Club course to finish a stroke above Argentina's Andres Romero and American Kevin Stadler. Two-time defending champion Phil Mickelson shot a disappointing 72 to fall eight strokes behind Johnson. Johnson, who started on the back nine, notched three birdies in his first five holes, featuring a monster 64-foot birdie putt on the 12th. He also converted birdie putts of 15 and 10 feet in his first nine. The 25-year-old needed less work for his birdies on the back nine, holing putts from a foot, 6 feet and 14 feet. More known for length in driving rather than accuracy on the greens, Johnson was ranked 62nd for total putts on the tour last year, and was 115th after two events this year. Although only turning pro in 2007, he has already clinched two titles, the 2008 Turning Stone Resort Championship and last year's Pebble Beach National Pro-Am. Three players - Alex Prugh, Rickie Fowler and Brett Lederer - were unable to complete their round due to failing light and will return to the play their final hole of the first round Friday.