The defender was drafted into the starting line-up as one of seven changes made by Di Matteo following the 4-1 Champions League win over Napoli in midweek.
Cahill, 26, joined the Blues in January in a £7 million deal from Bolton where he played alongside midfielder Fabrice Muamba - who is currently critically ill in hospital.
And Di Matteo admitted he had spoken to the England international prior to the match.
"We checked with him before the game," he said.
"He was shaken like the whole football community and our thoughts and prayers go to the family of Fabrice but he managed to focus on the game and had a very good game as well."
Cahill confessed his thoughts were elsewhere during the game but that was not evident from his performance as he opened the scoring in the 12th minute before revealing a T-shirt tribute to Muamba.
Fernando Torres then took centre stage as he scored a brace and made another two goals, breaking his 151-day scoring duck in the process.
Di Matteo was happy to see Torres get the monkey off his back, but also reckons he was never worried about the misfiring Spaniard.
He said: "I think the whole team, the club and supporters are happy. He works so hard for the team and he is a great team player. "Hopefully his confidence is going to be high - I didn't mind when he wasn't scoring because as long as we win as a team that is what matters to me"
The result means Chelsea have won all four games under Di Matteo since the Italian replaced Andre Villas-Boas, but the caretaker was not happy with all aspects of his side's performance against the Foxes.
"It was a wonderful team performance which is reflected in the scoreline, we just wanted to get to the next round," he said.
"We conceded two goals today [Sunday] and I look at that and think we could have done a bit better there but we are scoring goals and we seem more solid as a team.
"I always believe we have quality in the team to score at least one goal so, as long as defensively we can keep it tight and solid, we will always have a chance."