World No.1 golfer Yani Tseng tumbled dramatically out of contention during Friday’s second round of the Women’s Australian Open.

The Taiwanese star, who is aiming for a third successive Australian crown, plunged from the Royal Melbourne leaderboard.

Tseng began the day just a stroke off the pace and maintained her position even as the leaders began to pick up shots.

She was cruising after birdies at two of her first three holes when she struck a disastrous patch.

A bogey four at the fifth hole was followed by a four-over-par eight at the seventh and, by the time she left the eighth green with another bogey, she had handed back seven shots in five holes.

While Tseng dropped, young US Open champion So Yeon Ryu put together a four-under-par round of 69 to take a share of the lead at six-under.

She was tied with American Stacy Lewis while Ryu’s Korean compatriot Hee Kyung Seo produced a flurry of nine birdies and two bogeys to finish with a 66 and jump to five-under for the tournament.

Jessica Speechley was the leading Australian at two-under-par while joint overnight leader Sarah Kemp, from Sydney, collapsed to be seven-over after 10 holes.