Ajayi made his debut for the Super Eagles in their 2-0 defeat to Serbia in a friendly on March 27 in London.
In the game against Tanta, Ajayi opened the scoring for Al Ahly in the 61st minute before his teammate Marwan Mohsen doubled their lead on 86 minutes.
Tanta scored a consolation goal through Mohamed Gaber in the 90th minute.
Commenting on his goal, Ajayi wrote on Twitter: “Coming from international friendly and continue to mark my register is the way and only way to go. Up Al Ahly.”
The win took Ahly to an unassailable lead on 78 points while Tanta are 16th on 26 points in the league table.