Maher Hannachi put the club from Mediterranean resort Sousse ahead after 19 minutes of the matchday 4 clash in the 34 degree celsius (93 fahrenheit) heat of southeastern Nigeria.
Iheb Msakni converted a 69th-minute penalty to double the lead of Etoile, the only club to win all five current and past African club competitions.
Etoile have seven points, Sfaxien five, Enugu four and Salitas of Burkina Faso two in the section and the winners and runners-up qualify for the quarter-finals.
Record three-time Confederation Cup winners Sfaxien could regain top spot later Sunday if they defeat academy club Salitas in Ouagadougou.
Hannachi,a 34-year-old veteran of CAF club football with Sfaxien and Etoile, slammed the ball past Enugu goalkeeper Nana Bonsu from close range to put Etoile ahead.
The Tunisian attacker also played a role in the second goal as he was fouled by Isaac Loute and Msakni calmly scored from the spot.
Disappointing Enugu rarely threatened to score as they suffered a second successive loss to Etoile having fallen 2-1 in Tunisia last Sunday.
Twice Confederation Cup winners Etoile started their group campaign poorly, losing at home to Sfaxien and drawing away to Salitas without scoring in either match.
But the side coached by Frenchman Roger Lemerre have bounced back with the home and away victories over Enugu and are poised to secure a last-eight place.
Now 77 years old, Lemerre is the only coach to win the European (France in 2000) and African (Tunisia in 2004) championships.
Congo Brazzaville club AS Otoho Oyo boosted chances of a top-two finish in Group A by edging Moroccan visitors Hassania Agadir 1-0 in central town Owando.
Arci Saint Thibault Biassadila netted on 70 minutes for the Congolese to avenge a narrow loss in Agadir last weekend.
Renaissance Berkane have seven points, Otoho five, Hassania four and trophy-holders Raja Casablanca two in a mini-league that includes three Morocco clubs.
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