The 20-year-old Shibuno, a rookie on the Japan LPGA Tour who was making her LPGA Tour debut, birdied five of the final nine holes in a 4-under 68 and 18-under 270 overall.
Salas, who started the day tied for fourth, quickly played herself into contention with three birdies in the first four holes, and she added five more in a 7-under 65 at Woburn Golf Club.
But the American will regret not taking another birdie chance on the 18th when she shared the lead with Shibuno. It was Salas’ best finish at a major.
Jin Young Ko, seeking her third major title of the year after winning the Evian Championship last week, was third, two shots back after a bogey-free 66.
Morgan Pressel (67) finished fourth at 15 under, just ahead of early leader Ashleigh Buhai (70), whose hopes were dented Saturday when she let a five-shot lead slip. The 30-year-old South African finished fifth at 14 under.
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