* Korean Jang stays out in front
* Fifty-four players yet to finish second round (Updates after play suspended for the day)
July 17 (Reuters) - First-round leader Jang Ha-na fired a bogey-free four-under 67 to extend her lead at the Marathon Classic to two strokes when play was halted late in Friday's second round due to a threat of lightning.
Second-round play was suspended with 54 players still on the golf course.
LPGA Tour rookie Jang, still bothered by a back injury that has her finishing her golf swing with one arm, was ready to roll after a delay of more than two hours to the start of the round.
The 23-year-old South Korean, who led by one overnight, posted birdies on her first two holes and two more on her second nine, crowned by a 10-foot birdie at the ninth, her last hole of the day.
"I'm very happy today," Jang said. "You see my one-hand swing? Think it's better than my two-hand swing," joked Jang, who unlike Thursday was able to practise for 30 minutes to get loosened up before round two.
Fellow Korean Q Baek also shot 67 to reach the clubhouse at seven-under-par 135, two strokes behind Jang.
Another shot back were China's Shanshan Feng (67), Australian Sarah Kemp (69) and Dewi Claire Schreefel of the Netherlands (68).
Feng said conditions were more difficult on Friday.
"Fairways were really soft. Balls weren't releasing so shots into greens were longer than yesterday," Feng said. "It was a little bit tougher than yesterday."
At 137 was Moriya Jutanugarn of Thailand, the 2013 LPGA Tour Rookie of the Year, who also holed out her second shot at the par-four fourth hole for eagle on her way to a five-under 66.
Joining the fray was another injured player, world number 13 Lexi Thompson, who gave herself a fighting chance despite struggling late in the round with a wrist injury.
The long-hitting Thompson shot 67 to stand three under par, but last year's Kraft Nabisco winner grimaced in pain at the 17th and later revealed she has been suffering for months from an injury tied to a photo shoot for Golf Digest.
"It did happen boxing in the Golf Digest photo shoot," said the 20-year-old Thompson, who posed topless for the magazine's cover. "I'm not really a boxer, apparently.
"I ended up hyperextending my wrist and it's hurt ever since. It's been hurting for the last few months but I've just been trying to work with it and I've been getting treatment for it."