The former Bolton man was still reeling from the devastation of leaving the field with a hamstring injury on Tuesday night when he was joined by Terry, who inexplicably got himself sent off in the Blues' astonishing 2-2 second-leg draw at the Nou Camp.
Cahill said: "I was devastated that I had no more part to play in the game and, when I looked up and saw JT come through the door, I'll be honest, I probably feared the worst. But the lads were absolutely outstanding, the way they stuck together and ground out the result. It was amazing. Phenomenal, absolutely phenomenal."
He added: "I was about four times more nervous than playing, watching the game, just in the changing room praying that it would go all right and, luckily, in the end it did."
Terry's moment of madness - the Chelsea captain kneeing Alexis Sanchez from behind eight minutes before half-time - looked to have been fatal, with Barca having already levelled the tie before going 2-0 up on the night.
But Cahill and Terry then witnessed the 10 men produce one of the most heroic displays in the history of European football to secure a draw and win 3-2 on aggregate.
Having initially disputed his sending-off after taking an age to leave the field, Terry eventually held his hands up.
"I've seen the replay and it does look bad," he told Sky Sports 2. "I'm not that type of player to intentionally hurt anyone. I've raised my knee, which I maybe shouldn't have done in hindsight.
"I'm disappointed but delighted for the lads. I've apologised to them and I want to apologise to the fans as well. At the time, I was bewildered because I was trying to protect myself a little bit, but looking at it on the replay, I've no complaints. I've let the lads down. They've performed brilliantly, so hopefully this doesn't take it away from the players.
"This is what this football club deserves. We deserve to be in the Champions League final."
Source: PA
Source: PA