* World number two sits nine shots off the lead
* Hopes of three wins in as many weeks all but dashed (adds quotes, details)
By Ian Ransom
MELBOURNE, Nov 21 (Reuters) - World number two Adam Scott's hopes of winning the World Cup of Golf for Australia plunged midway through his opening round on Thursday when he crashed to a quintuple-bogey nine at the par-four 12th at Royal Melbourne Golf Club.
In red-hot form and coming into the revamped tournament on the back of two wins in the last two weeks, Scott had been heavily backed to take individual honours and guide Australia to victory in the team component.
The U.S. Masters champion started steadily enough, grafting through breezy conditions to be one-under at the turn.
Things came dramatically unstuck for the U.S. Masters champion at 12, however, when he sprayed two tee-shots into a tangle of bushes on the right of the fairway.
Unable to find his first ball, Scott returned to the tee and put his third drive into light rough before over-cooking his approach and seeing his shot roll over the green.
Needing to get up-and-down for eight, Scott missed his putt from about 12 feet to post his worst single-hole score in a U.S. PGA Tour-sanctioned event since his 10 at the WGC tournament at Doral Golf Resort in 2007.
"Just a couple of lazy swings today on... 12, and, you know, paid the price," Scott said greenside. "Just away with the fairies on that hole."
Scott hit back with a birdie on the next hole, but fell away again with a bogey on the par-five 15th and finished with a four-over 75 to be joint 46th in the field of 60, nine strokes behind joint leaders Kevin Streelman of the United States and Denmark's Thomas Bjorn.
Playing his third tournament in three weeks following wins at the Australian PGA Championship in the Gold Coast and the Australian Masters at Royal Melbourne on Sunday, Scott has also had a whirlwind of media appearances and sponsor events in his first trip Down Under since his Augusta triumph.
"Could be (fatigue), but, you know, it was a little disappointing to do that but stuff can happen and that's why when you play good tracks like this you need to be switched on at all times and I paid the price today... Other than that is was fairly solid," he added.
There was some cheer for local fans as a grieving Jason Day battled to a three-under 68 to sit two shots behind Bjorn and Streelman.
The world number 18 is mourning the loss of eight relatives who were killed when Typhoon Haiyan pounded the Philippines earlier this month, and his five-birdie round left Australia six strokes behind the leading United States and Denmark in the team component of the tournament.
Sixty players are competing for individual honours while 26 two-player teams are going for the team prize according to their aggregate scores. (Editing by John O'Brien)