In his first game on the bench, the Portuguese coach guided the Porcupine Warriors to a 4-0 home triumph in the outstanding matchday 16 fixture at the Len Clay Stadium in Obuasi.
Brazilian playmaker Fabio Gama Dos Santos scored his second goal in two games, compatriot Michael Vinicius netted on his Kotoko debut while centre-back Ismail Abdul Ganiyu and striker Francis Andy Kumi also added their names to the score sheet.
“I am not happy. We should have won by eight nil or nine nil. We created many chances that we should have scored more," Barreto said at the post-match press conference after the game.
"I think if we take so many chances of clear goals today, it should have been eight or nine goals.
“They tried today to do what we are hardly training on. We don’t have time and they have to understand that in football, there are rules and there are disciplines.
"They are getting used to it, so we will need a little time. Not that because we have scored 4-0, now we are heroes, no."
Barreto was appointed Kotoko coach last month, granting him a return to Ghana for the first time since managing the West African nation's national team between 2003 and 2014.
He assumed duty ahead of Saturday's 1-1 away draw with Eleven Wonders but was forced to watch the game from the stands due to a delay in the completion of his work permit.
“They made a good team today, there are many things that we have to improve and I know they are trying. Look, our best striker left and from the defence we have to improve a little to be better," the 64-year-old said.
"In the midfield, Mudasiru [Salifu] is not completely fit and we have some problems in the team because we have about six players out, even before I came in and some of them are key players.
“We win 4-0 and of course I should be happy but only today. Tomorrow we start our work.”
Kotoko have moved to the third position on the league table by Wednesday's result, just ahead of archrivals Hearts of Oak but behind leaders Great Olympics and Karela United.
The 23-time GPL champions are looking to win the title again for the first time since 2014. Read Full Story