Both sides started red-hot from beyond the three-point arc, both making four of their first six attempts from long range, as Siauliai finished the opening period with a 29-25 lead.
The hosts increased the gap to 46-40 at the halftime break, with newcomer Bambale Osby performing well and providing the Lithuanian side a much-needed inside presence.
Siauliai led by as many as nine points in the second half, but Pyrinto’s go-to duo of Kelvin Lewis and Benjamin Raymond made sure to keep the Finns within reach of their opponents.
A pair of free-throws by Travis Leslie had increased the home side’s advantage to 82-78 with only a couple seconds to spare, but a three-pointer by Yannick Anzuluni just before the horn cut it to one point.
Arnas Labuckas paced the winners with 16 points, while Vytas Sulskis, Travis Leslie and Bambale Osby all finished with 13 points apiece.
For Pyrinto, Kelvin Lewis had a game-high 21 points, Antero Lehto scored 17, while Benjamin Raymond chipped in with 16 points and five rebounds.