The 19-year-old New Zealander, who won the ANA Inspiration in April to add to her victory in the Evian Championship last September, shot a one-under-par 70 at Washington’s Sahalee Country Club today to put her on two-under after three rounds.

Ko’s closest challengers are the American duo of Brittany Lincicome and Gerina Piller, both of whom shot level-par rounds to sit one-under.

"It seems like the girls, they're playing really well, and they're playing consistent," said Ko, who will take a lead into the final round of a major for the first time in her career

"I've just got to focus on my game.

"And I can't control what the other girls are doing.

"So just try my best out there.

"We've still got a long 18 holes to go.

"You just never know what's going to happen until the winner's putt drops on the last hole."

Lincicome is content with her position going into tomorrow's final round, saying: "It's easier to come from behind than be the leader.

"I feel like I'm in a great spot.

"Hopefully I just keep driving the ball like l have been doing all week.

"My game feels really, really good."

South Korea’s Amy Yang was the big mover of the day as she posted the lowest round of the week, a five-under 66, to move into contention.

The 26-year-old is two shots back in a tie for fourth spot with compatriots Chella Choi and Mirim Lee, Canada’s Brooke Henderson, Thailand’s Ariya Jutanugarn and Sweden’s Anna Nordqvist. 

Second-round co-leaders Henderson and Lee each shot 73, meaning only three players are under par.

Thirteen players are within three shots of the lead, however.