By Tony Jimenez

VIRGINIA WATER (Reuters) - Paul Casey showed no mercy on a listless Colin Montgomerie on Saturday, going five up on his Ryder Cup team mate midway through their 36-hole World Match Play Championship semi-final.

American Shaun Micheel was one up on Swede Robert Karlsson, who will be making his Ryder Cup debut in Ireland next week.

Casey, winner of the China Open and Johnnie Walker Championship titles earlier this season, only had to play steady golf to reach the turn four up on Montgomerie at Wentworth.

The 43-year-old Scot, who complained of tiredness after his 36-hole win over Michael Campbell on Friday, struggled to an outward half of 38, three-over-par.

Montgomerie fell further adrift when World Match Play debutant Casey played a majestic six-iron tee shot at the short 10th and holed out for his third birdie of the round.

Three putts cost the 29-year-old Casey the 11th but Montgomerie went back to five down four holes later when he missed the green with his approach and failed with his par-saving effort from 10 feet.

Casey moved six up when he struck a five-wood to the heart of the green at the par-five 17th and rammed in his 16-foot putt for an eagle.

But Montgomerie prompted loud cheers from the gallery by holing an 18-foot birdie putt to win the 18th. He went round in 74, two-over, while Casey carded a 68.

Micheel, who knocked out Tiger Woods and Luke Donald earlier this week, made an untidy start as Karlsson went two up after four.

Karlsson bogeyed the eighth and 12th to allow Micheel to get back to all square before the 2003 U.S. PGA champion birdied the 18th to edge ahead.

Micheel recorded a 73 while Karlsson had a 72.

The four players are chasing the richest first prize in golf, one million pounds.