Steve Bruce's men earned their seventh win in a row to move into the automatic promotion spots, with Hourihane sealing the win with a stunning effort.
Bruce only returned from compassionate leave after the death of his father a day earlier, and the shed a tear as his side captured the lead on the hour mark.
As the ball was launched into the box in the last few moments of the match, the Birmingham midfielder went up for a challenge with Mile Jedinak.
Twitter reacts to LeBron James raining on Paul Pierce's parade
James gave Cavs fans a scare when he left the game after suffering an apparent right leg injury late in the first quarter. The 10-time NBA All-Star played 15 seasons in Boston, winning the one Finals series and playing in another in 2010.
Goals from Albert Adomah and Conor Hourihane condemned the Blues to their 17th defeat of the campaign, with only Burton Albion and Nottingham Forest losing more times than Cotterill's side.
Here is a selection of the best reactions from Aston Villa fans from his first-half performance.
Aston Villa were victorious in today's second city derby against Birmingham City, thanks to two second half goals. "We have the future to take care of". "He will pick the team and we will be ready without his presence this week, but his presence is always there with the players anyway".