By Norman Dabell
NEWPORT, Wales (Reuters) - German Marcel Siem shared a one-shot lead after Friday's Wales Open second round in which the Celtic Manor Ryder Cup venue proved the day's real winner.
Siem was the first to hit the front on six-under-par 136 with a four-under 67 to be joined late in the day by Australian Andrew Dodt, who posted a 70. The pair lead by a stroke from Dane Thomas Bjorn (68).
The top three were among the few who proved immune to mishaps over the Twenty Ten course that will host the match between Europe and the United States in October.
Overnight leader Chris Wood of Briton tumbled down the field, five shots off the pace, with three double-bogeys on his card of 76.
Scotland's 1999 British Open champion Paul Lawrie ran up a sextuple-bogey 11 on the long second, using up eight putts as his ball kept returning to his feet from the uphill green.
World number 12 Martin Kaymer of Germany clocked up eight strokes on the par three third, twice hitting into water.
While Lawrie missed the cut, Kaymer rallied to card a 74 and make the weekend on two-over 144.
Europe's Ryder Cup captain Colin Montgomerie came through the second round relatively unscathed as he posted a 70 to lie only four shots off the lead.
Montgomerie, who has had a hand in the course changes, acknowledged how difficult the Twenty Ten course could be as double-bogeys littered the cards.
"I heard about Paul and I saw Martin Kaymer put two in the water," Montgomerie told reporters. "It was a very difficult day. The course has won the first two days here."
World number nine Luke Donald also spoiled his day with a double-bogey on the 18th.
However, last week's Madrid Masters champion was in bounce-back mode again as he recovered from a first round 75 to equal the course record 65 in moving to two-under. Donald sunk putts of 40, 30 and 25 feet and three putts from 20 feet.
(Editing by John Mehaffey)