UPDATE 1-Golf-South Korean Ji birdies last to win U.S. Open

* Ji sinks 20-foot putt to birdie 18th for win

* Kung's final-round 69 leaves her one shot back

(updates after final round)

By Larry Fine

BETHLEHEM, Pennsylvania, July 12 (Reuters) - Ji Eun-hee of South Korea rolled in a 20-foot birdie putt on the last hole to win the U.S. Women's Open for her maiden championship title on Sunday.

The 23-year-old Ji's downhill putt at the 18th completed an even-par 71 for a level-par 284 total which beat Candie Kung of Taiwan by one stroke.

"I was extremely nervous before that last putt," Ji told a television interviewer after thrusting her arms up in triumph on the last green.

Kung, who began the day five strokes behind overnight leader Cristie Kerr, fired a two-under-par 69 for 285.

Kerr, the 2007 champion who had led the tournament after the second and third rounds, had trouble avoiding the rough on Sunday and finally relinquished the lead when her four-foot par putt at the 13th lipped out.