Britain's Richard Kilty produced a stunning run to win 60m gold at the World Indoor Championships in Sopot.
The 24-year-old held off a field including Nesta Carter, the fifth fastest man ever over 100m, and much-fancied American Marvin Bracy to win in a personal best time of 6.49 seconds.
"I can't believe it. This is a dream come true," said Kilty.
Tiffany Porter won Britain's first medal of the three-day competition with bronze in the 60m hurdles.
Britain were fancied to win medals in the final two events on day two, but Kilty's gold was a big surprise.
The Gateshead Harriers athlete was competing in his first major championships, having been drafted in to replace the injured James Dasaolu.
He qualified easily for Saturday's semi-final, where he finished second to Jamaica's Carter to make the evening's final. There he was expected to trail 2012 silver medallist Carter again, but instead the Teessider blew the Jamaican and the rest of the field away, going under 6.50 seconds for the first time.
The Briton had improved on the 6.53 secs he ran at the British Indoor Championships in Sheffield last month with a 6.52 in his semi-final in Poland, and took a further three-hundredths off in the final.
He finished ahead of Bracy, who took silver in 6.51 secs, and Qatar's Femi Ogunode, who claimed bronze. Kilty's team-mate Dwain Chambers was sixth in 6.53, with Carter coming home seventh.
Kilty said victory meant he had "proved selectors wrong" for omitting him from the team for the London Olympics in 2012. He had run an 'A' standard time of 20.50 secs in the 200m, but Team GB selected only Christian Malcolm and James Ellington for the event.
The British sprinter then experienced more misfortune when he suffered a torn hamstring and struggled without any funding. However, fitness and performances improved in 2013 and as a consequence he was restored to the funding programme in October.
"For the last few years all I have done is get slated by the media and people in my home country," he added.
"I considered quitting because I had no income and had to train on the road in trainers. I couldn't afford to get to the track. Nobody's had it harder than me last year.
"Thankfully my dad Kevin persuaded me I had the talent and told me to give it another year, and this is for him and all my fans and supporters."
Earlier, Porter added a bronze to the 60m hurdles silver she won at Istanbul 2012.
The American-born athlete was edged out of silver spot by defending champion and outstanding pre-race favourite Sally Pearson, with the USA's Nia Ali taking gold in 7.80 secs.
"It wasn't my best performance," Porter told BBC Sport.
"My start was awful, which was frustrating because that's one of the better parts of my race. All of us know you never go out there thinking who ran what earlier. It's all about delivering on the day - Nia showed that."
There was disappointment for the British team as Luke Cutts of Sheffield could only finish eighth in the pole vault. The 26-year-old broke a 12-year-old British record in January with 5.83m, but only managed 5.65m in Poland.
Elsewhere, America's Ashton Eaton successfully defended his heptathlon title after finishing just 13 points short of his own world record.
In the women's 1500m, Sweden's Abeba Aregawi won gold comfortably by a 6.51-second margin.
But just one centimetre separated gold and silver in the women's triple jump, with Russia's Ekaterina Koneva pushing Ukraine's Olga Saladukha into second place with a 14.46m leap.