It was the first victory this year for the 17-year-old Ishikawa, and it came at the right time. The top four players not already exempt for the British Open earned a spot in the field July 16-19 at Turnberry.
"I'm thrilled to have qualified for the British Open,'' he said. "There were some tense moments today but it all worked out in the end.''
He took a quintuple-bogey 9 on the 12th hole, then rebounded with a chip-in for eagle on the 16th. He closed out his round with a birdie to finish at 13-under 275, three shots ahead of David Smail of New Zealand.
Ishikawa won for the third time in his career, and the second time as a pro. He became the youngest winner of a sanctioned tour when he won the Munsingwear Open KSB Cup at 15 two years ago.
Ishikawa missed the cut this year at the Masters, where he was given a special invitation. He also has received an invitation to the PGA Championship in August at Hazeltine National Golf Club in Minnesota.