UPDATE 1-Golf-Open-Barnes retains narrow lead at Bethpage

* Leader Barnes charges six ahead before slipping back

* Woods again struggles with putter en route to a 68

* Mickelson trails by seven after carding a 69 (Updates at end of third round)

By Mark Lamport-Stokes

FARMINGDALE, New York, June 21 (Reuters) - Surprise package Ricky Barnes kept his cool to cling on to a one-shot lead when the rain-delayed U.S. Open third round was completed at Bethpage Black on Sunday.

A stroke in front midway through the year's second major, the American PGA Tour rookie raced six ahead before losing momentum after the turn on the way to a level-par 70.

Barnes, who came through 36 holes of qualifying last week to book his place at Bethpage, posted an eight-under total of 202 in pursuit of his first victory on the U.S. circuit.

He rolled in a 25-footer to birdie the par-three 17th before bogeying the last after hitting his approach into tangly greenside rough and failing to get up and down.

Compatriot and playing partner Lucas Glover also returned a 70 to lie second, four shots ahead of former world number one David Duval (70) and Britain's Ross Fisher (69).