Diaz, who also played for the club as a striker, was appointed last week after Matias Alymeda stepped down, although reserve team coach Gustavo Zapata took charge of the team against Lanus last weekend.
It took until the second half on Sunday for Diaz to be able to celebrate his team's first goal, with Manuel Lanzini opening the scoring on 59 minutes and Carlos Sanchez doubling the lead six minutes later.
As the league reached its halfway point, Independiente and Colon Santa Fe played out an entertaining 2-2 draw that saw the home side finish with 10 men.
Osmar Ferreyra gave Independiente the lead after just two minutes, but Emmanuel Gigliotti scored twice in four minutes early in the second half for the visitors.
Ernesto Farias equalised in the 64th minute for Independiente, who had Samuel Caceres sent off in the last minute.
The day's other game between Lanus and San Lorenzo finished goalless.