Ranked 39th in the world, the United States' Ewing sank six birdies in her first 11 holes on the way to finishing with a six under par total of 66.

Another birdie on the 16th hole helped to cancel out a bogey on the last to give her the impressive 10 under score after the opening two rounds. 

"I didn't know until I signed my scorecard that I had four birdies in a row, so I'd probably say that stretch from 6 to 11 was a little bit of a blur," Ewing said.

"But I was very in-the-present on all of those shots.

"It's not like [my mind] was wandering around, it still took execution and being in the present."

Ewing's closest challengers at the midway stage are Toronto 2015 Pan American Games silver medallist and compatriot Andrea Lee and Japan's Minami Katsu.

Both of them currently sit on five under par with scores of 68.

Regardless of her strong position, Ewing is not getting ahead of herself and is determined not to let complacency set in.

"I'm gonna know where I'm at [on the leaderboard] at the end of the day, but mentally you just have to be ready to regroup because the past is the past," said the 30-year-old.

"Nothing I've done in the past 36 holes can do anything for me for the next 36, so I'm just going to be mentally prepared for each individual day that presents itself."

Some of the sport's top stars are struggling so far in the Open.

Frenchwoman Celine Boutier came into the tournament with high expectations after victory at the Evian Championship but shot 71 on the second day putting her one over par overall.

Former top-ranked player Lydia Ko, currently ranked number five, made five bogeys in her opening 10 holes and was looking like missing the cut.