Zamalek's victory avoided a North African derby in the next stage - by finishing top of the group, the Egyptian side will play Tout Puissant Mazembe in the semi-finals.
Mr Maduro recently said the president was "battling on" and had entered a new stage of treatment, after successfully finishing the post-operative phase.
American Mark Miller came in third, and remains third overall, after finishing four minutes 22sec behind Sainz on the stage and is now 28min 12sec behind overall.
Ameobi admitted their achievements at this stage have surpassed pre-season expectations, and revealed that finishing the job is now his and his team-mates' priority.