Enyimba will take a 1-0 lead when they visit Rivers United in the return leg of the CAF Confederation Cup playoff next weekend in Port Harcourt.
The overall winners of this matchup will advance to the money-spinning stage of the Confederation Cup.
The all-Nigerian clash was only decided in the 59th minute through midfielder Cyril Olisema.
The game was held up for several minutes after heavy downpour after nine minutes of action.
Enyimba were reduced to 10 men in the 75th minute, when striker Tosin Omoyele was sent off.
The home team dominated the tie, but could not make their dominance to count with more goals.
The visitors chased the game in the closing moments.
The loss in Aba has denied Rivers United a 20 million Naira promise by Governor Nyesom Wike.