The 44-year-old Johnstone birdied two of the last three holes for a 14-under par total of 274 to claim the winner's cheque of £85,000.

Karlsson could have forced a play-off but his eagle chip on the last slid past the hole and the 31-year-old had to settle for a closing 73 and outright second place - his best finish since winning the Belgacom Open in 1999 - and a cheque for £56,000.

New Zealand's Elliot Boult was two shots further back in third with France's Olivier Edmond and Scotland's Dean Robertson joint fourth on nine under par.

Former Open champion Paul Lawrie slumped to a closing 79 after damaging his putter on the fifth tee following a double bogey six on the previous hole.

Johnstone, trailing by one after the third round, got off to the perfect start, chipping in for an eagle on the par five first hole to jump into a one shot lead over Karlsson, who was playing in the group behind.

The pair both bogeyed the fifth before Karlsson picked up a birdie at the ninth to get back on level terms and after another pair of dropped shots at the 14th, the decisive moment came when Johnstone birdied the 16th.

That restored his one shot cushion and another birdie from 15 feet on the 18th effectively sealed victory, Karlsson missing his eagle chip and the following birdie attempt to finish two adrift.