Chambers, who was only given the green light to qualify for London 2012 after a legal ruling forced the British Olympic Association to drop their lifetime ban for convicted doping cheats, has endured a miserable season so far.
His season's best ranks him only eighth in the UK and it's one tenth of a second shy of the A standard he needs to run - and finish in the top two in the 100m final at the Aviva 2012 Trials tomorrow - to guarantee selection.
Adam Gemili and James Dasaolu, the only two athletes to have achieved the 10.18 sec selection mark, both progressed through their heats at the Alexander Stadium in Birmingham.
Chambers was second quickest overall in 10.34 secs while rising star Gemili underlined his growing reputation, seemingly running within himself to clock 10.27 secs.
"I’m just trying to not pressurise myself at all," said Chambers. "It’s going to be tough with the young boy there. I know he’s in good shape and situations like this are when I run my best, so I’ve got to be at my best.
"I hope I’ve got an A standard run in me this weekend. Main thing is to get through the championships in one piece and hopefully that enables me to secure the qualifying time.
"Normally I’m the one on the top so it is a bit daunting being lower down. Things have happened that haven’t allowed me to have a smooth ride, I’ve just got to put that to one side and do the job this weekend."
Meanwhile, Anyika Onuora was quickest into the women's 100m semi-finals in 11.48 secs while Ashleigh Nelson, Montell Douglas and Abi Oyepitan were not far behind. So far only Oyepitan and Laura Turner, who is not competing in Birmingham, have run the 11.29 sec A standard.
Elsewhere, Phillips Idowu joined fellow championship medallists Hannah England, Jenny Meadows and Yamile Aldama on the absentee list from Birmingham.
The former world triple jump champion has struggled with form this season and hasn't competed since suffering an unspecified injury during the IAAF Diamond League meeting in Oregon earlier this month.
It means he will now need to rely on the selectors discretion to make the Olympic team, although UK Athletics head coach Charles van Commenee did not appear concerned about the situation.
He declined to discuss Idowu's exact problems due to issues of 'medical confidentiality' but added: "It's not a worry. He is selectable."
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