Paralympic debutants Tully Kearney, Reece Dunn and Toni Shaw claimed medals for Great Britain on day one of the swimming at the Tokyo Aquatics Centre.
Kearney was denied gold in the S5 200m freestyle in heart-breaking fashion after leading throughout before defending champion Zhang Li snatched victory at the last with a winning margin of just 0.12 seconds.
Dunn also had to settle for silver in the S14 100m butterfly as Brazilian Gabriel Bandeira pipped him to first place with a Paralympic record of 54.76.
Earlier, 18-year-old Shaw won ParalympicsGB’s first medal of the Games in the pool, clinching bronze in S9 400m freestyle with a lifetime best of 4:39.32.
Kearney was forced to withdraw from Rio 2016 because of injury before being reclassified a year later due to the progression of her generalised dystonia, a neurological movement disorder that causes uncontrollable muscle spasms.
She looked set make up for lost time in Wednesday’s penultimate race as she powered into a healthy lead which, for a long time, was world-record pace.
The 24-year-old tired in the final length and, despite posting a personal best time of 2:46.65, Chinese swimmer Zhang stole the ultimate prize, while fellow Briton Suzanna Hext was fourth.
“There was a question mark over whether I’d ever get to a Paralympic Games and the fact that I’ve been able to race and come away with a medal is crazy,” Kearney told Channel 4.
“I thought after Rio, the Paralympics wouldn’t be possible, I wouldn’t be able to swim any more, so this is obviously a massive deal and it’s all down to the amazing support staff, the amazing team – I just swam.
“I’ve not had that much training, I’ve been dealing with injuries and things; I was nervous my fitness wouldn’t be good enough to swim 200 so to go that close was pretty impressive and I’ve got to be pleased with that.”
Plymouth Leander swimmer Dunn – the world record holder – finished 0.36 seconds adrift of Bandeira after falling short as he battled to overhaul his rival during a hard-fought second length.
The 25-year-old had underlined his gold credentials as the fastest qualifier, setting a Paralympic record of 55.99, which he and, crucially, Bandeira then subsequently broke in the final.
“I’m a little bit disappointed with my finish, I lost it there, but still happy nonetheless,” he said.
“I knew it was going to be a tough race coming in and it was going to go down to the last five metres and he obviously beat me to it.”
Scottish swimmer Shaw was a convincing third-placed finisher in her race, touching the wall more than seven seconds ahead of fourth-placed Australian Ellie Cole.
She was 2.64 seconds behind the silver medallist, Hungarian Zsofia Konkoly, with Australia’s Lakeisha Patterson taking gold by the narrowest of margins.
Elsewhere, Britons Louise Fiddes and Jessica-Jane Applegate missed out on podium places in the S14 100m butterfly, finishing fifth and sixth respectively as Russian Valeriia Shabalina romped to gold in a world-record time of 1:03.59.
Paralympic champion Ellie Robinson, who will defend her 50m butterfly title next week, opted to withdraw from the S6 50m freestyle ahead of the heats in order to focus on her other events in the competition.