It was funny because of our immense failings at maths. We thought he only had three turns before Yuna got a turn - so we defended three times, which was perfect because he only had enough HP for those three turns, and he had a whole 3HP left. Scraped by! We breathed a sigh of relief and mashed X to get Yuna to Holy the Demonoliths to death.
Then Tidus jumped forward and died after missing his attack, because we couldn't count and it turned out he actually had four turns before it was Yuna.
It's not funny when you tell the story. But there it is.