Dynamo St Petersburg trailed BC Khimki until late in the third quarter but finally took control to win 92-81 and reach the championship game of the FIBA Europe League.
Playing in Istanbul and looking to remain unbeaten, Dynamo encountered stiff opposition in an all-Russian affair but got their noses in front with just 10 minutes left and pulled away.
They stayed in front for the remainder of the contest.
Melvin Booker, Khimki's veteran guard from Mississippi, led all scorers with 30 points while Serbo-Montenegrin Ognjen Askrabic paced St Petersburg with 28 points and 11 rebounds.
Khimki led by as many as seven points at 49-42 after a pair of Booker free throws with a minute and 11 seconds remaining in the first half.
St Petersburg hit back after the interval, though, and tied the game after a mistake on the perimeter by Venezuelan international Oscar Torres.
The former Pompea Napoli star fouled St Petersburg's Kelly McCarty while he was attempting a three-pointer.
McCarty sank all three free throws to level the contest at 51-51.
A Booker lay-up put Khimki right back in front, but the lead would end up changing hands several times in the period, the last when Stefansson made his jumper to put his side in front for good at 67-66.
David Blatt's team them pressed home their advantage.
St Petersburg's other starting guard, Ed Cota, scored and was fouled. The former North Carolina Tar Heel converted the three-point play for a four-point edge.
Cota, after Vasily Karasev missed a three-pointer, was fouled again, this time by Karasev, and he made two more shots from the line to stretch the lead even further.
St Petersburg would end up leading by as many as 13 points before sealing the win.
McCarty weighed in with 18 points and Cota chipped in 15 with eight assists.
Argentinian international Ruben Wolkowisky scored 15 points and hauled down 11 rebounds in defeat for Khimki.