The win saw the Latvian side improve to a 2-4 record, while Tarvas held on to the third place in Group B despite dropping to 3-2.
Although the visitors from Estonia led by as many as seven points in the first half, Jurmala/Fenikss brought things level before the interval, with teams tied at 31-31.
In the third quarter, Jeromanovs and Casey Roberts were clicking for the home side, who gained a double-digit advantage at 59-48 with a dunk by Endru Smits just before the buzzer.
Tarvas were not ready to give up, though, and mounted a comeback in the fourth quarter, taking a 68-66 lead with 46 seconds left in regulation after seven points in a row by Roberts Stumbris.
A big three-pointer by Jeromanovs had given Jurmala/Fenikss a 70-68 lead, but Reinis Sturpovics sent the game to overtime with a game-tying drive with just over a second left.
After a sub-par performance in the fourth quarter, Jurmala/Fenikss dominated in the extra period, outscoring the guests 20-4 to finally put an end to the losing streak.
Jeromanovs finished the game with a game-high 30 points and seven assists, while Maris Ziedins added 12 points and five rebounds. Roberts Stumbris led Tarvas with 20 points and 11 rebounds.