The former champions wasted no time separating themselves again.
Kerr had a chance to regain a share of the lead at No. 15, but her makeable eagle putt slid just by on the left, and she and Pettersen both had short birdie putts, giving the leaders some breathing room.
Kerr, who made several tester putts to save par during her round, pulled even on the par-4 16th, rolling in another from inside 10 feet for birdie after Pettersen's longer birdie attempt missed.
Both parred in, with Pettersen's long birdie try at No. 18 missing right by half an inch, and Kerr having to make yet another tester, this one from about 6 feet, to force the sudden death playoff.
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