I don't have any max-level healers, so it was not *my* clutch healing moment, although it was my clutch tanking moment.
I had just finished leveling my now-main rogue (switched from a feral to help the guild, not only but in part due to the legendaries). I do not remember if she had a bit of heroic FL gear, or maybe just the head and trinket from a Rag kill on monday, but even so, she was really not well geared.
It was ZA, bear boss. The tank died, god-knows-why, with the boss at 70%. I didn't notice the boss health, otherwise I might have given up right there. The moment the boss turned to me, I hit evasion, used a 5-CP Recuperate, and continued dps'ing. It was then that I saw the boss health, still above 50%, and the disc priest at less than half his mana. My only thought was 'wipe', but I kept on tanking the boss. Evasion ended with the boss at a bit more than 30%. I went so close to death many many times, was saved more than once by a tick of Recup, and the healer was completely OOM, but we killed the boss.

After it was over I typed on party chat 'Plate tanks are overrated' XD