Proteas EKA AEL went on a decisive 15-2 run over a span of seven minutes in the second quarter and used that as a platform for victory over visiting Khimik.
Looking to make the EuroCup Final Four for the first time in their history, the Cypriot club won at home in Limassol 70-65 and will attempt to close out the best-of-three quarter-final series next Tuesday in Ukraine.
Khimik, who got 14 points apiece in the game from Wykeen Kelly and Sasa Bratic, encountered a slow-starting Proteas who trailed 15-6 late in the opening quarter.
Ryan Randle's tap-in closed the gap to 18-16 with 10 minutes gone.
After Olumuyiwa Famutimi made it 20-16 in favour of Khimik when play resumed, Duane Woodward sparked Proteas into life with a three-pointer.
Ali Bouziane scored down low to take his points haul to seven before captain Milutin Aleksic added back-to-back lay-ups.
Bratic stopped the bleeding with a made jump shot for Khimik, only for the hosts to score six more points in a row for a 31-22 lead.
The closest Khimik would get the rest of the way was four points.
That happened two minutes into the final quarter when Oleksandr Kolchenko drilled a three-ball to reduce Khimik's deficit to 52-48.
A killer blow then struck the Ukrainian team when Famutimi was whistled for a foul on Vasily Zavoruev, who was attempting a three-pointer, and he made all three of his shots from the charity stripe for a seven-point lead.
Kelly did give Khimik hope with an incredible four-point play midway through the quarter.
But the reliable Aleksic responded with a lay-up to take his points haul to 18 as Proteas stayed in front for the remainder of the game.
Aleksic had 21 points for the winners, who won despite being out-rebounded 42-31.
Duane Woodward also had 15 points and four assists in a winning effort.
Proteas did force Khimik to turn the ball over 18 times while losing possession themselves on just 11 occasions.
Charles Barton, Proteas EKA AEL Coach-
"It was one our toughest tests so far. Khimik is a great team but we played really well. If we play our next game that way we will go in the final four. Our fans were great tonight and we need them each game".
Duane Woodward, Proteas EKA AEL-
"It was a great game. The first period we started off slow. There was a lot of emotion and energy. We had great defence throught out the game! We had a lot of support from the fans. They were just fantastic!"