KASAMA, Japan - Ryo Ishikawa had the worst round of his professional career on Thursday with a 12-over 83 at the Japan Golf Tour Championship.

The 19-year-old Ishikawa had six bogeys, an 8 on the par-4 14th hole and a triple-bogey on the par-4 17th. His only birdie of the day came on the par-5 sixth hole.

He finished the day tied for the third worst score with three other golfers.

Masanori Kobayashi, who defeated Ishikawa in a playoff at the Totoumi Hamamatsu Open two weeks ago, took the lead with a 2-under 69.

Ishikawa has an exemption for the June 13-19 U.S. Open.