David Biton’s all-important goal earned the White Star their first points in Group K and maiden victory against English opposition.
While both teams ended the match with 10 men after Osman Chavez was sent off for the home side, the decision to dismiss Dembele midway through the first half changed the match.
The Belgium international was sent off for retaliating to a clip on the heels from Gervasio Nunez and will receive a one-match ban.
“I was angry,” Jol said of the decision. “If you are in control and lose a player that is a normal feeling. That changes everything. After seeing it, of course it is wrong as he raises his hand but you can’t say it is a push.
“You could say it was a frustrating evening. Before the sending off I think we were in control. The pace was good, possession play was good and I was very satisfied. Then we got a straight red card and that makes it difficult for any team. Even after that we should have had a couple of decisions. You can’t say anything about the referee, bad or good.”
Sheffield Wednesday defender Tom Lees could return to the starting line-up for the home game against Ipswich.