Having kept the 12-point margin in the second quarter, the visitors began to struggle after the halftime break, with Jekabpils eating into the double with a 10-0 run late in the third period to get within 49-50.
Despite losing the double-digit advantage, Valmiera managed to stay in front, but the Troy Barnies-led Jekabpils stayed close, trailing only 60-61 with five minutes left in the game.
With just over a minute on the clock, the hosts were down only by two points, but a three-pointer by Janis Kaufmanis increased the gap to 73-68, giving the visitors the final push towards the victory.
Janis Kaufmanis paced Valmiera with 30 points, Viktors Iljins scored 11 points and grabbed 13 rebounds, while Raimonds Gabrans scored 10 points.
Troy Barnies had a team-high 23 points and added nine rebounds for Jekabpils, Cameron Runders had 12 points, while Pavels Veselovs chipped in with 11 points.