The American was a shot off the lead at the conclusion of the first round before hitting a four-under score of 68 to clinch a two-shot lead in the third major of the year.

"I think that's something that is just so special," said the 26-year-old playing in her rookie Ladies Professional Golf Association season.

"I'm honestly just enjoying the moment here.

"I'm trying not to get too ahead of myself." 

Tardy has missed five cuts and withdrawn once in 10 events so far this season before sealing her place at Pebble Beach through a qualifier.

Her best finish was a tie for 23rd place at the Lotte Championship in Hawaii in April.

In California, she picked up four birdies and eagled the par-five sixth hole for the second straight day which helped up make the cut for the first time in her four US Women's Open appearances.

Tardy's compatriot Allisen Corpuz and Evian Championship winner Kim Hyo-joo of South Korea are both two behind the leader following scores of 70 and 71, respectively, in the second round.

Kim was on course to maintain her day one lead but finished the round with two consecutive bogeys.

South Korea's world number one Ko Jin-young suffered a shock exit after missing a 25-foot birdie putt on the 18th hole meaning she missed the cut by one stroke on score of 151.

Lilia Vu of the United States, winner of the first major of the year the Chevron Championship, could not beat 79 in the first two rounds, also failed to advance. 

Others who missed the cut included Vu's countrywoman Michelle Wie West and Annika Sörenstam of Sweden, the President of the International Golf Federation.

Both were playing in their final edition of the Open and stopped to hug each other prior to the 18th green before scoring 79 each.

"It was great to have my last round here at Pebble Beach," said 33-year-old 2014 winner Wie West, who made history 20 years ago by becoming the youngest player to make the cut at the US Women's Open.