Anna Nordqvist had 68 strokes with her from the first day.
But after a double bogey on hole 14, her second round landed on 74 strokes and she fell to a split 29th place, a total of two under par.
Best Swedish for the third round of the Chevron Championship in California is now instead Madelene Sagström, who is in shared 20th place with three under par.
She has kept an even class both days and followed up the first day's 71 strokes with a second round of 70 strokes.
Pernilla Lindberg is on par and qualified by a kind of margin for the last two days' games.
The Chevron Championship, which is played at the Mission Hills track in Rancho, is one of five major competitions for women and has a prize pool of five million dollars, equivalent to 46 million kronor.
In the lead alone after the second round is 23-year-old Japanese Hinako Shibuno, who went around 66 strokes and is a total of nine under par.
She is being chased by a trio that is a blow behind: the American shoes Jennifer Kupcho and Annie Park and Patty Tavatanakit from Thailand.
CLIP: Anna Nordqvist aims for more major wins (December 21, 2021)
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REPORTAGE: Anna Nordqvist aims for more major wins