Montgomerie lost four of the first six holes
Colin Montgomerie edged to a dramatic final-hole win over defending champion Michael Campbell to reach the World Match Play Championship semi-finals.
The Scot now meets England's Paul Casey, who beat Canadian left-hander Mike Weir 5&3 at Wentworth.

The other semi-final will be between Shaun Micheel and Robert Karlsson.

American Micheel, who beat Tiger Woods in the opening round, won 4&2 against Luke Donald while Swede Karlsson saw off Angel Cabrera 4&3.