UPDATE 2-Alpine skiing-Aerni wins men's combined gold by slimmest of margins

* Aerni takes surprise combined gold

* Austrian favourite Hirscher takes silver

* Swiss winner has yet to stand on World Cup podium

* Home nation has three golds from six races (Adds quotes, detail)

ST MORITZ, Switzerland, Feb 13 (Reuters) - Swiss surprise Luca Aerni dethroned Austrian favourite Marcel Hirscher by the slimmest of margins to win men's combined gold on home snow at the Alpine skiing world championships on Monday.

Aerni, just 30th after the opening downhill - a position that meant he went first out of the start hut on the Suvretta slalom piste - beat 2015 champion Hirscher by 0.01 of a second in a total time of two minutes 26.33 seconds.

The Austrian, a five-times overall World Cup champion who started third in the slalom after ending the downhill in 28th place, had to settle for silver.

Switzerland's Mauro Caviezel took bronze, on a course set by a Swiss coach, with a combined time 0.06 slower than the winner.

"I was really nervous the last 45 minutes waiting for everyone to finish," Aerni said after taking the first medal of a hitherto unremarkable career. "I could only watch and hope as the others came down.

"I knew my slalom run was good, but with the combined you never know what will happen," added the surprised 23-year-old who has yet to finish higher than fifth on the World Cup circuit.

He had been sure of his position on the Swiss combined team only on Sunday night.

The gold was host nation Switzerland's third in six races at the championships, with Aerni matching the women's combined gold won by Wendy Holdener on Friday. Beat Feuz won the men's downhill on Sunday.

Austria's Romed Baumann, a combined bronze medallist on home snow in Schladming in 2013, was fastest in the downhill but his 30th start position in the slalom worked against him with the snow softening in bright sunshine. The early leader finished 12th.

The top 30 skiers from the downhill started the slalom in reverse order with the medals decided on total times from the two disciplines.

The slowing surface was criticised by France's Alexis Pinturault, one of the big pre-event hopes who faded badly in the slalom.

"Really disappointed," he told Eurosport television. "The slope is just a joke. They didn't prepare it for today. They prepared it only for the downhill and not the slalom." (Writing by Alan Baldwin; Editing by Robin Pomeroy)