Di Matteo did acknowledge the two thrilling clashes with Manchester United - the league fixture was followed by the nine-goal Capital One Cup tie in midweek - may have hurt his side.
He said: "We have certainly felt (tired) this week after the two games with Manchester United, including extra-time.
"It would have been great to finish off the week with a 1-0 victory. The disappointment is we have conceded a late equaliser.
"I thought we had more of the game and clear chances than Swansea.
"When the opposition equalises so late on then you tend to think it's a bit lucky.
"To be honest, they didn't have any real clear chances, but they scored a quality goal."