Nadir Belhadj drilled home the decisive kick after Ryohei Hayashi's effort was saved to complete an amazing 12 months for Qatar, who were named as hosts of the 2022 World Cup last December.
Reysol struggled in attack on a chilly night despite being tidier in their build-up play with Al Sadd equally toothless.
Shots were sliced horribly wide for throw-ins before Ibrahim Majid went close for the Qatari side with a dipping free-kick in the 74th minute.
European champions Barcelona later beat South American champions Santos 4-0 in the final to win the competition.
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