Golf: Chaotic back-nine sees Lydia Ko lose pace with leaders at LPGA's US Open

A catastrophic back nine has left Lydia Ko with plenty of work to do at the LPGA's US Open, sitting at an even par 70 after the first round in San Francisco, four shots behind the leaders.

Beginning her day with three straight pars on a course that saw some of the big names struggle, Ko surged into contention with a birdie on the fourth hole.

Another par on the fifth, before Ko shot back-to-back birdies on the sixth and seventh, moving as high as a tie for second place.

But at three-under and within touching distance of the lead, Ko's round came apart within the space of two holes.

On the 13th, Ko dropped her first shot of the day with a bogey on the par three, before disaster on the par four 14th hole. 

Finding the rough with her tee shot, it took Ko's second and third shots to find the green, giving her a distance putt to save par. But her effort came up short, before her attempt at bogey kissed the rim of the cup - forcing her to tap in for a double bogey.

Within two holes, Ko had slipped from three under to even par.

Another bogey on the 16th moved Ko to one-over-par, seeing her slip further down the leaderboard.

But to her credit, a long range birdie putt on the 17th brought Ko back to even par, and narrowly missed the chance to finish with back-to-back birdies on the 18th, making par to finish with an even 71.

The Kiwi is in a 12-way tie for 16th place, alongside the likes of Thailand's Ariya Jutanugarn.

Ko is chasing the leading trio of England's Mel Reid, Canada's Brooke Henderson and American amateur Megha Ganne, 17, both finishing their first rounds after shooting a four-under 67 each. 

Fellow Kiwi Amelia Garvey shot a first-round 74, and sits three over par in a tie for 57th in her second US Open, in her first Major as a professional. 

This is Ko's first event since taking a break from golf at the start of March, missing the Pure Silk Championship in Virginia and a Las Vegas matchplay event to prepare for the US Open.

Ko is hoping to win her first Major since 2016 at the US Open, with her last triumph coming at the 2016 ANA Inspiration.