British diving star Tom Daley survived a poor preliminary round in the 10m platform to edge through to Saturday's semi-finals.
A disappointing start was compounded by a sloppy fifth dive to leave him in 16th place with a round to go.
The 18-year-old did just enough with his final dive to move up to 15th, with the top 18 in the 32-man field progressing.
Team-mate Peter Waterfield could only finish 23rd and is now out.
"That will not be good enough for Pete Waterfield, what an absolute shame. He will not be progressing, it was such a tough day out there. There were some glaring errors, his second round only scored 40 points and really cost him. He's out, that's a real shame for this four-time Olympian."
Waterfield, who won a silver medal in the 10m synchro at the 2004 Olympics, was in second to last place after two rounds.
The 31-year-old gave himself a chance with a superb third dive and solid fourth effort, but the inconsistency returned in round five and his Olympics are now over.
He told BBC Sport: "It wasn't meant to be for the whole of the Olympics. I've been training well for a long time but it's about what you do in competition and that was just terrible."
Daley, the sport's poster boy, has been in good form this season, claiming three second-place finishes and a first in the World Cup Series.
But the teenager never looked happy on Friday and his fifth dive was one of the worst of his usually spectacular career, a 39.60 for a backward three-and-a-half somersault.
A score of 84.15 in the sixth round put some gloss back on his display but he will need to improve to make the final.
"If I was going to have a bad competition, today was the best to do it on," he said. "It was definitely the worst I've dived all year.
"It's nerve-wracking because you don't know what is going to happen. In my last dive, it was now or never and thankfully I made it."
Daley's Chinese rival Qiu Bo had guaranteed his qualification after five rounds and finished a massive 115.25 points clear of Daley's total.
Bo's Chinese team-mate Lin Yue was second, with only Germany's Sascha Klein getting anywhere near their consistency.
The scores are wiped clean for Saturday's semi-finals, which begin at 10:00 BST, with 12 advancing to the finals at 20:30.