The turn of events was a dramatic echo of his injury-induced withdrawal from the same stage of the Beijing Games four years ago.
The 2004 Olympic champion and former world record holder hit the first hurdle with his lead leg and tumbled to the ground before being helped from the track with his dream of regaining the title in tatters.
The heat was won by Britain's Andy Turner in 13.47 seconds with a total of four athletes failing to finish.
China's first male gold medallist on the Olympic track, Liu remains one of his country's most popular and high-profile sportsmen alongside former basketball player Yao Ming.
The 29-year-old is still plagued by the Achilles injury that forced him to pull out at the Bird's Nest in Beijing but he had hit a rich vein of form this year.
A blistering run of 12.97 seconds in his hometown of Shanghai was his first run under 13 seconds in five years and he backed that up with a 12.87 run in Oregon, which would have tied the Dayron Robles's world record but for an illegal wind.
The first indication that the injury demons might have returned came when he pulled out of last month's London Grand Prix, "a precaution" his camp said.
On a cool morning in London, China's vast media corps had streamed into the Olympic Stadium and waited expectantly for the sixth and final heat only for Liu to make another untimely departure.
A supreme technician in the high hurdles, Liu barely even brushes the barriers during a race so it is likely that injury, nerves or a combination of both contributed to such a major error.
Liu's biggest rival, Cuba's defending champion Robles, had earlier looked comfortable as he eased into the semi-finals in 13.33 seconds despite missing most of this season through injury.
American Aries Merritt, the form hurdler this year with three runs of 12.93 seconds, stormed through to win his heat in 13.07 seconds, the fastest first-round time at an Olympics.
His compatriot and world champion Jason Richardson, who has also run under 13 seconds this year, won his heat in 13.33.
Pozzi, 20, only managed to clear one hurdle before feeling his hamstring, which he injured in the build-up to the Games, and he trudged off the track a disconsolate figure.
His frustration was clear for all to see but he insisted he was ready to run despite not being fully fit.
“I was so disappointed,” said Pozzi. “It’s all we’ve been waiting for all year. We trained so hard through the winter months and this is the aim – this is what it’s about and to leave like that was heartbreaking.
“The last month since Crystal Palace has been a nightmare. I tore my hamstring in the final there and I just haven’t been able to get it sorted. I was really optimistic, but it’s gone.
“I always knew I’d run and I feel so privileged to be here. That’s the first time I’ve been out of the blocks since Crystal Palace and we thought we’d try and give it a go but it didn’t come off.
“I hope I’ve got more to come but you don’t know that until it happens. I’ll go back to training, try and get this healed and then hopefully I can do it instead of talking about it.”
Experienced hurdler Turner admitted nerves got to him before the race, as he has struggled for form, but felt good about his run.
And he also had sympathy for Chinese star Liu.
He said: “It felt relatively easy to be honest. I was absolutely petrified before I went out there as I've been struggling for form all year, but training has been great for the last two weeks so I just need to keep the wheels turning.
“I noticed in Crystal Palace during the warm-up that Liu was rubbing his Achilles. I knew then that he had a problem and in warm-up I knew he was not quite with it.
“In the race halfway through I looked to my left and noticed he wasn’t there. It’s a shame because I’ve got a lot of respect for him.
“I really feel for him because he’s such a great athlete. With an Achilles injury you can’t run on your toes. It’s hard to run with that kind of pain.”
Lawrence Clarke finished second in his heat – also in a time of 13.42 – to qualify for the semi-finals and was happy to have got his campaign underway in a solid fashion.
The 22-year-old admitted he used the experiences of not qualifying 12 months ago at the world Championships in Daegu as motivation for his heat in London.
“I’m so relieved if anything,” said Clarke. “You come on that start line – it’s the first round and people won’t remember you if you go out in the first round.
“In Daegu I went out in the first round and coming through the mixed zone was the worst experience of my life.
“I came out in tears there – I had a clean race, which is what I was determined to do here, that’s what I’ve done and hopefully I can be more prepared for the semi.
“I’ve dreamt of this moment for the last four years and I was determined not to come to the start line and make a hash of it.”