A 4-0 win over lowly Cibalia gave Rijeka a five-point lead over Dinamo with only one match each to play.
Swiss forward Mario Gavranovic set them on their way with two goals in the first quarter of an hour, Roman Bezjak added a third before the break and Dario Zuparic completed the scoring in the second half.
Rijeka, who will enter the Champions League in the second qualifying round next season, became only the fourth team to win the league following Dinamo, who have 18 titles, Hajduk Split and NK Zagreb.
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They have previously won the Croatian Cup three times and the old Yugoslav Cup twice. (Writing by Brian Homewood in Berne, editing by Pritha Sarkar)
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