St George rugby league star Lance Thompson made a successful debut as a professional boxer and promptly declared it was the hardest thing he had ever done.

The Dragons second-rower and vice-captain won a majority points decision in an exciting four-round heavyweight contest against journeyman Huso Smajlagic, aka The Big Eagle.

Two of the judges made him the winner by a margin of three and four while the other gave Smajlagic a one-point victory.

Most of the bout, fought over two-minute rounds, was conducted at close quarters with both men landing and copping plenty of right-hands.

Thompson enjoyed a height advantage after weighing in at 98.5kgs, almost two kilos heavier than his opponent.

The Dragons star stressed it was a one-off for charity and believed he had raised $15,000 for the Children's Hospital at Randwick and the St George Foundation through sponsorship.

"It was tough and hard and in the end maybe my fitness got me over the line," said Thompson, who was cheered on by the crowd which included most of his clubmates.

"I thought definitely I was probably the stronger in the end. It was the hardest thing I had to do, he never hurt me," added Thompson.

Smajlagic, who is a Canterbury Bulldogs rugby league supporter, suffered his 11th loss in 15 professional fights.

He gave Thompson an instant lesson as the St George star extended his glove at the very start of the fight only to be met by a barrage of punches in return.

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