Diouf, who made his name when his country shone at the 2002 tournament, was in the stands in Moscow as Aliou Cisse's men defeated Poland 2-1 in their first World Cup game since that event 16 years ago.
Thiago Cionek's own goal and a second-half strike from M'Baye Niang proved enough for the African side, despite Grzegorz Krychowiak's late response for Poland.
Former Liverpool forward Diouf was sitting a few rows back from the dugout and was the first to stand and applaud the Senegal players who were substituted in the closing stages, all of whom acknowledged his support as they left the pitch.
And a joyful Diouf told Omnisport after the match: "It is a perfect start for us.
"It is a great result and also performance. But the big tests are now to come in this group."