He went straight to Karon Police Station where officers reacted quickly and caught the thief at his home in Chalong with the tourist's telephone still in his pocket.
Alexander Bakhnov, 26, said he was staying at The Palmery in Kata with the door to the pool left open as he prepared for bed.
About 12.30am he noticed the telephone, valued at 13,000 baht, had disappeared from a table.
Police checked security camera footage and used a motorcycle ownership data base that put them on the doorstep at the southern Phuket home of Tung Taotong, 28, before sunrise.
In his pocket was Mr Bakhnov's telephone, police said. Shown the security camera footage, he admitted the theft.
Police are still looking for a man so far identified only as ''Ae'' who kept lookout for Khun Tung while he stole. It's expected that security at The Palmery will be improved.