On a day when all the 14 teams were in action, Brazilian striker Loks scored a goal in the 70th minute to help the OPL leader extend its lead to five points from its nearest challenger Dhofar.
After the 18th round of games, Al Shabab, which took over as the league leader in December, has maintained its grip and now has 39 points after 11 wins, six draws and one loss.
The only defeat Shabab suffered this season was on October 27 when it lost 0-2 to Sohar at the Seeb Sports Stadium during the eighth-week action.
Coached by Salim Sultan, who succeeded Waleed al Saadi after the latter was drafted by the Oman Football Association (OFA) as deputy to national team coach Pim Verbeek at the start of the year, Shabab has been one of the most aggressive teams with 30 goals to its credit.
Only thirdplaced Al Arouba has a better goal-scoring rate with 32 goals. It is the fourth win in a row for Sultan, who has won all the four OPL games so far, with the team scoring a total of ten goals.
Nine-time champion Dhofar remains in second place after its latest 2-1 win over Al Nasr, while Al Arouba, despite a 1-3 loss to Sohar, is third with 31 points.
All the matches played on Sunday produced results, with hosts Al Nahda scoring an upset 2-1 win over defending and nine-time winner Fanja at the Buraimi Sports Complex.
Al Khabourah scored a crucial 3-0 win over Oman at the Sultan Qaboos Sports Complex (SQSC) to stay above the relegation zone, while Muscat edged past Al Rustaq 2-1.
Former champion Al Suwaiq was the biggest winner of the night as it registered a 4-1 win over Saham, which continued its slide following its defeat in the first leg of the His Majesty's Cup semifinals to Dhofar last week.
Both the teams are also representing Oman in the AFC Cup, the second-tier club competition in Asia.
Standings [after 18 rounds]: Al Shabab (39 pts), 2 Dhofar (34), 3 Al Arouba (31), 4 Sohar (29), 5 Al Nahda (26), 6 Fanja (26), 7 Saham (24), 8 Suwaiq (23), 9 Al Nasr (22), 10 Muscat (21), 11 Al Khabourah (20), 12 Rustaq (16), 13 Oman (16), 14 Jalan (13).