Karlo Vragovic made four free throws in the final 24 seconds to give Croatia a 76-70 victory in Group F of the U20 European Championship.
Vragovic scored 18 points for Croatia, who improved to 2-1 in Group F of the qualifying round while Bojan Bogdanovic added 13 points, Matej Karlovic had 12 points and Miro Bilan chipped in 11 points.
Croatia star Mario Delas finally played his first game of the tournament, scoring all eight of his points in the final 11 minutes of play after nursing an injury from the FIBA U19 World Championship.
Sead Sehovic paced Montenegro with 19 points, six rebounds and five assists while Nikola Djokovic scored 17 points and Nikola Vucevic collected 16 points, four rebounds and five blocks.
But it was not enough for Dejan Radonjic's team, which dropped to 1-2 in the group.
Croatia led 13-10 midway through the first quarter when Vucevic and Filip Barovic combined for seven points in a 12-2 run which had Montenegro leading 22-15 after one period.
Montenegro did not let up in the second quarter and Sehovic gave Radonjic's team a 35-24 lead. But Croatia held Montenegro scoreless for the final four minutes of the first half in going on a 9-0 run to close within 35-33 at intermission.
Croatia continued their surge in the second half, out-scoring Montenegro 12-3 for a 45-38 advantage. And it was 50-43 after Karlovic's three-ball. Vucevic again sparked a run with two baskets and Nikola Ivanovic's three-ball gave Montenegro a 52-50 lead.
But Marijo Hajdic nailed a long ball and Delas scored his first basket of the tournament as Croatia were up 55-52 after three periods.
Delas hit two straight baskets and pushed Croatia ahead 61-53. And Bogdanovic hit a three-ball and completed a three-point play to keep Darko Kunce's team up 67-61 with just over two minutes to play.
Sehovic's triple cut the gap to 70-68 with 30 seconds remaining before Vragovic hit four foul shots and Djokovic missed a three-pointer and Montenegro turned the ball over in the final 15 seconds.