Golf-Ailing Day tees off in U.S. Open third round

* Day finds fairway with opening tee shot * Looked frail during his warm-up (Adds detail, byline) By Mark Lamport-Stokes UNIVERSITY PLACE, Washington, June 20 (Reuters) - Australian golfer Jason Day, who sent a scare through the U.S. Open on Friday when he collapsed due to vertigo on his final hole, teed off in the third round on Saturday after resting overnight. The world number 10, who has a history of dizzy spells, was diagnosed with benign positional vertigo after receiving medical treatment following Friday's second round at Chambers Bay. Day looked a little frail after arriving at the practice range exactly an hour before his tee time and he blinked repeatedly in between shots under a blazing sun. After working his way up from bunker shots to irons and drivers, he knelt by his golf bag while talking to his caddie before setting off to the shuttle area where he was transported to the first tee. Warmly applauded by the galleries packed around the par-four opening hole, Day struck his tee shot safely down the fairway. One of the pre-championship favourites to win the year's second major, the Australian generated the biggest storyline on Friday when he collapsed on his final hole before getting to his feet, completing the second round and collapsing again. Day had played a bunker shot on the par-three ninth, before two-putting for bogey and an even par 70, which left him just three shots off the lead. "His condition is being monitored closely and he is hopeful he will be able to compete this weekend in the final rounds of the U.S. Open," Day's manager, Bud Martin, said in a statement late on Friday. (Editing by Gene Cherry)