The 23-year-old Dubliner appeared poised to extend the match by stealing an error-strewn eighth frame. But after an impressive shot from brown to blue, he missed the latter ball, giving Hendry an unexpected lifeline.
"Fergal was under a bit of pressure," said Hendry, who went on to win 5-3. "But I really felt it was going to go to 4-4. Having said that, I looked like I was going to have a fairly comfortable win until I missed a black off its spot to go 4-1 up."
Instead, O'Brien recovered from 48-26 down in the fifth with a 35 clearance and Hendry admitted: "From that point I stuttered over the line."
A five-day break from the tournament did Hendry no favours, although he was not looking for excuses after ensuring three Scotsmen - Alan McManus and John Higgins are the others - will contest the semi-finals. "I've been a professional long enough not to let it bother me," Hendry added.Reuse content