Great Britain let a 15-point lead and a potential ticket to the Olympic basketball quarter-finals slip as they went down 106-75 to Australia.
Britain led 51-36 early in the second half, putting them in command of their own destiny as a win followed by victory over winless China would have put them through.
But in a final 19 minutes coach Chris Finch described as "surreal" Australia outscored Britain 70-24 to grab that final quarter-final berth in Group B.
"Of course it surprised me," Finch said of Australia's second-half performance. "Seventy points in a half is not typical, it's not the way we try to play defence."
Finch admitted Britain's 46-36 half-time lead was probably not a true reflection of the game, but he still did not expect it to change quite so dramatically.
"I thought if there was any bit of deception in the game it's that we scored pretty easily in the first half," he said. "We knew they would tighten up.
"We knew the physicalness was coming. We thought we could handle it better than we did.
"When the floodgates opened we tried switching line-ups, switching match-ups, tried going big, tried going small, but we couldn't get it under control.
"That's something that happens but it was a bit surreal. I don't think there were 30 points in the game but that doesn't really matter now."
Britain could hardly have asked for a better first half as Dan Clark came off the bench to score timely threes and Joel Freeland caused Australia's big men plenty of problems.
Freeland, who finished with 16 points, scored the first five of the second half and it looked as if Britain's strong play would continue.
Instead, Britain were torched by Australia's electric guard Patty Mills, who scored 25 of his 39 points in the second half and inspired a stunning turnaround.
"Congratulations to Australia on reaching the quarter-finals," Finch added.
"That's certainly a place we thought we could get to, but we didn't play 40 quality minutes. We were hurt by some old demons, our inability to handle pressure and cheap threes really turned the game around."
Finch was left frustrated by the officiating in the second half as Britain could not get a break from anywhere, but some of the decisions of his own players were just as disappointing.
"We just needed a couple of buckets, some finished lay-ups, there was another missed goaltending call in there," Finch said of Australia's surge.
"We just need anything at that point to break it up. But by then it was on. They got in one of those zones where everything goes in."
Australia led 66-60 by the end of the third quarter, then killed it off completely by scoring the first 18 points of the fourth.
"It's very frustrating and disappointing," said Drew Sullivan. "We came into the game understanding the task at hand.
"We played really well in the first half, but we didn't take care of business in the second half.
"We had the opportunity to stay with them if we made some lay-ups, but some of the threes they hit changed the game.
"It's bitterly disappointing."