CJ Ujah, Zharnel Hughes, Richard Kilty and Nethaneel Mitchell-Blake won Team GB silver in the 4x100m relay at Tokyo 2020.
Led by 100m individual champion Marcell Jacobs, Italy secured the gold medal in a captivating race as Filippo Tortu dramatically stormed past Mitchell-Blake in the final few metres to finish just 0.01s ahead.
Great Britain ran a season's best 37.51s and went into the final leg with a slender lead but it was not enough to top the podium.
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Jacobs, Tortu, Lorenzo Patta and Eseosa Desalu set a new national record with 37.50s to continue the Italians' stellar track and field campaign.
Canada's quartet of 200m champion Andre De Grasse, Aaron Brown, Jerome Blake and Brendon Rodney claimed the bronze medal with a season's best 37.70s, as Canada and the USA missed out on the podium.
Ujah, 27, from Enfield, said: "I'm used to doing that now. I've been doing it this whole cycle - a long cycle, five years.
"To round it off with a silver medal - I feel we've collected a medal at every major championships as a team. I'm super proud of these guys."
Hughes, 26, from Anguilla, said: "Tonight was all about giving it our all. I knew CJ [Ujah] was going to come in fast tonight.
"My body is feeling well, and I gave it everything. We've always been dreaming about this moment and it came to pass."
Kilty, 31, from Stockton-on-Tees, said: "After the heat we knew we had to pull it out and give it our everything, we would do anything - what more can we ask for?
"We're Olympic silver medallists. In Rio, we finished fifth and so we wanted a medal, we went to win it but we were unlucky.
"This is unity and a team and we're in this together and we absolutely pulled it out as a quartet to win this medal. And in 20 years' time we will look at this as one of the best moment of our lives."
Mitchell-Blake, 27 from Newham, said: "Apologies if I seemed ungrateful at first.
"We put a lot of work and effort into this and we believe we're the best quartet in the world and we wanted to display that when the time comes.
"We want to show the world we deserve to be on the platform we are."
It is Italy's fifth gold medal in athletics, after the 100m, high jump and men's and women's 20km walk race.
The men's silver medal came just moments after the women's team of Dina Asher-Smith, Daryll Neita, Asha Philip and Imani-Lara Lansiquot won a bronze medal.