Pettersen, ranked No. 3 in the world, finished 54 holes at 14-under 202. Eun-Hee Ji (64), Inbee Park (69) and overnight leader Morgan Pressel (71) are second at 205..
There was a one-hour, 12-minute weather delay. It was anticipated that play would stop for about 20 minutes, but when the golfers returned a large boom of thunder made golfers wait sat for almost 45 minutes longer, before then completing the round.
"We are kind of getting used to it out here," said Pettersen, a five-time winner on the LPGA Tour whose victories all came last year.
Hee-Won Han had a 64 on Saturday and is tied for fifth place at 207 with Ai Miyazato, who shot a 1-under 71 in the third round.
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