The 28-year-old, who won the Meijer LPGA Classic last week, holds the 54-hole lead in a major for the first time in her career.

Maguire would have had a bigger advantage had she not dropped her second shot of the day at Baltusrol at the 17th.

However, she two-putted from distance at the last, also a par five, to regain the stroke to sign for a 69 - her eighth successive round in the 60s - and edge her back in front on seven under.

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It put her one ahead of Japan's Jenny Shin with Northern Ireland's Stephanie Meadow a further shot back after a 67 moved her up to five under.

"It was a little bit more of a mixed bag then the first two two days but I felt I hung in well," Maguire, who had four birdies in addition to her two bogeys, said in her post-round interview.

"It's always nice to finish with a birdie. The gameplan is the same as the last three days, if it's enough, it's enough. My game's in good shape."

On potentially being the first Irish winner of a women's major she added: "I know it would mean a lot but I try not to get too ahead of myself. Whatever will be, will be."

England's Mel Reid, who finished the second around just a shot off the lead nine months after quitting the sport, found the going tough on day three as she slipped to two over after a 77, which included a one-stroke penalty for deliberately lifting her ball after not realising it was not on the green at the fifth.