The Warrnambool golfer shot a one-over-par-71 in the opening round of the AT&T National in Philadelphia, leaving him tied for 49th with 17 other players.

Leishman, 26, finished yesterday with four bogeys and three birdies.

"I haven't seen rough this thick ever, which is good, because it rewards good play and punishes bad play," he said before the tournament.

Australian Jason Day wasted little time relocating his golf game as he vaulted into a share of the lead after round one.

Returning to action after a three-week break due to a severe sinus infection, Day carded a four-under-par 66 at Aronimink.

He joined Americans Joe Ogilvie and Nick Watney and Indian Arjun Atwal in a share of the lead - all four frontrunners playing in the more benign morning conditions.

Aaron Baddeley was best of the other Australians on 69, while Robert Allenby shot a respectable 70 in fluctuating afternoon winds.

Despite missing a tiny putt at the 12th hole, Allenby fared better than Tiger Woods, who played in the group ahead.

World No. 1 Woods drove the ball particularly well, but putted poorly down the stretch, dropping four shots in the final five holes for a dismal three-over 73.

"I just putted awful," Woods admitted.

"It was a very frustrating day on the greens, especially (considering) how good I was driving it. I was driving it on a string all day."

In May, 22-year-old Day became the youngest Australian winner on the US PGA Tour when he claimed the Byron Nelson Championship.

But two weeks later he was physically spent and pulled out of US Open qualifying to return to his Texas home and seek further treatment for his sinuses, which have been blocked for several months.

"I couldn't wait to get out here again," Day said after a round that included just one bogey, a three-putt at No. 10.

"After I won I played two more weeks and was getting a little burnt out. I'm a lot hungrier now.

"I hit a fair amount of fairways and a lot of greens today and when I missed a green I was in the right spot and able to get up-and-down.

"Other than the three-putt, it was really good."