Having already clinched a spot in the Last 16, Roanne do not want to lose any of their momentum and Lewis helped them notch victory against Kyiv with a terrific display in a key first-half stretch.
Trailing 16-14, Roanne got a three-ball from Lewis to claim a 17-16 advantage at the end of the first quarter.
He followed that with two consecutive three-point plays early in the second frame for a 23-16 lead.
The 9-0 Lewis spurt put the visitors in front to stay.
Kyiv managed to close the gap to one on two occasions in the second quarter but went to half-time trailing 49-41.
The game remained close and Kyiv even managed to claw the deficit back to 62-60 with 2:41 left when Denys Lukashov made a lay-up.
Pape-Philippe Amagou followed with a lay-up of his own, though, and Ralph Mims added a jump shot to settle the Roanne nerves.
They held on for a five-point win.
Mims had 15 points and Lewis 14 for Roanne, while Lukashov had a game-high 17 in defeat for Kyiv.
Kyiv are now 2-3 - the same record as KK Zagreb - and must win their remaining game at Keravnos to make certain of progressing to the Last 16.
Dmytro Bryantsev, BC Kyiv:
"We did a good job in defense, but our offence was really bad. We missed too many open shots from outside, that's why we lost the opportunity to grab this win."
Jean Denys Choulet, Roanne coach:
"I think that both teams did a good job tonight. For us it was very important to play good defense from the first instance and we did it. It was the key to our success. In my opinion BC Kyiv has better chances to qualify next round than Keravnos or KK Zagreb."
Nicholas Lewis, Roanne:
"For us it was really important to play good defens. Because of the weather we had a very long trip to Kyiv, we lost a lot of energy but tonight we showed character and showed a good game to reach our goal."