Veteran Winston Gordon lit up North Arena 2 with an ippon win over Alexandre Emond of Canada in the first round of the under-90kgs at ExCeL.
Londoner Gordon, 36, who just missed out on bronze from the Athens Games in 2004, delivered a much-needed boost for Team GB's judokas when he executed a perfect Tai-otoshi body drop to dispatch the world number 14.
Edinburgh's Sally Conway competes at under-70kgs, in the first round against Carine Ngarlemdana of Chad.
However, she is in the same pool as second seeded Dutchwoman Edith Bosch, the double Olympic silver medallist.
Conway, 25, was also looking to reach the last 16, which would put her within one victory of a shot at the medal fights this afternoon.
There was again plenty of support for the home judoka, whose attacking forced the Chad fighter into conceding a passivity penalty.
Conway moved further ahead midway through the contest with scoring throws of her own to take command and closed out victory with a holdown.
Team GB are looking to end a 12-year wait for a judo Olympic medal, since Kate Howey won silver in Sydney.
Gordon - who is sensei at the EB Phoenix Judo Club in Tooting - was next up against Russian Kirill Denisov, coming out to another standing ovation from the British crowd.
The three-time Olympian had to be on his guard against the shorter number seven seed, and was caught by a Yuko score after one minute and 15 seconds.
Lifted by chants of "Winston" from around the arena, Gordon went back on the offensive.
However, he still trailed 1-0 heading into the final 30 seconds and went out by the narrowest of margins to end another British judoka's Olympic dreams.
Gordon felt he could be proud of his efforts against the Russian, who was third at the 2012 Paris Grand Slam.
He said: "It was a tight match against a left-hander, which was very awkward. He caught me with a little counter and then locked up the shop, but he is an experienced fighter and is no mug.
"I put everything I could into the fight, but he kept it tight."
Gordon praised the "fantastic" atmosphere in front of a home crowd.
He said: "It took me back to the 2002 Commonwealth Games in Manchester. The crowd were phenomenal, they came in numbers to support me, family and friends, guys came over from Spain to support me and give me a good roaring on."
Gordon will take time to decide his future.
"The battle in itself was getting here," said the Londoner, who earned his place in the GB squad on appeal to the BOA.
"We have to sit back on the mat and discuss things over the next couple of months."
The North Arena was buzzing again when Conway walked in for her second-round contest just after 11:30.
However, the Dutch fighter, ranked second in the world, was a step up in class, having claimed the European title earlier this year.
However, to her credit, Conway went on the attack, but found her attempts at getting the right grip quickly countered.
There was no score heading into the last two minutes, but Conway then picked up a shido penalty for backing off.
A wazari score from Bosch followed, to leave Conway facing elimination unless she could produce a wonder throw in the final 25 seconds.
The big score never came, and again despite a morning of initial promise, Britain's judo hopes were again extinguished before the afternoon medal session.