Teenage swimmer Ahmed Hafnaoui stunned the Tokyo Aquatic Centre to become the first African to win a gold medal at the 2020 Olympics after a shock triumph in the 400m freestyle.
The 18-year old, who had been the slowest of the qualifiers for the final, produced one of the biggest surprises of the Games so far as he beat Australia's Jack McLoughlin, who won silver, and Kieran Smith of the USA, who took bronze.
Hafnaoui arrived at the Olympics with a time that was 15th best of the field and only qualified for the final in eighth place, putting him in the less favoured outer lane eight.
But he swam hard from the start and produced a brilliant final 50 metres to tap the wall in first. His winning time of three minutes 43.36 was three seconds faster than his personal best.
"I was surprised I was a finalist and now I am surprised to get gold," Hafnaoui said.
"I believed it when I touched the wall and I saw myself first. I was so surprised. I didn't expect that."
Hafnaoui is now only the second Tunisian to win gold in a swimming event in the Olympics, after double champion Oussamma Mellouli - who will be swimming the 10km marathon later in the competition. And his role in the Games is not over, as he will also compete in the 800m freestyle on Tuesday.
The title is Tunisia's fifth Olympic gold medal.
"I was (had) in tears in my eyes - when I saw the flag of my country and I heard the anthem in the background it was great. I am so proud of it," Hafnaoui said afterwards.
"When I hit the water, I just thinking about winning the medal not the time, and to go faster than yesterday,"
"I saw the Australian guy in the second 200m, I feel (felt) great in the water, it was a great fight in the end."
Analysis: Celestine Karoney, BBC Africa Sport in Tokyo
400m freestyle Olympic champion Ahmed Hafnaoui cut an emotional figure as the Tunisian national anthem rang out at the Tokyo Aquatic centre in Japan.
The 18-year-old Olympic debutant upset a strong field to win his first Olympic title and Africa's first gold of this Games. His performance was one of the outstanding results during swimming's morning session and got rousing applause from the few teams at the Aquatic Centre - as fans are not allowed at these Games.
And the 18-year-old isn't done just yet - he has an opportunity to build on his medal tally on Tuesday, when the 800m freestyle returns to the Olympics for the first time in a century.
On paper, this is Hafnaoui's stronger race - he is ranked eighth overall, and today's result has set him up as a medal contender for the longer distance.
The Tunis-based athlete began swimming at the age of six when his father Mohammed registered him at a swimming club after they went by a pool one day. Twelve years on, he has won his country's fifth Olympic gold medal, which he dedicated to his family and building on the legacy of the country's first Olympic gold medallist Oussamma Mellouli.
Mellouli, who will compete at the tail-end of the Games, was the first swimmer from Africa to ever win an individual gold medal in the Olympics. He has three Olympic medals to his name and has said Tokyo will be his last Games - and in Hafnaoui there seems to already be a passing of the baton for Tunisian swimming.
"I have a great relationship with Mellouli - he wished me luck before the race, and I guess I wish him luck in 10k in the open water," Hafnaoui said after the final.
"He is a legend - I wish to be like him one day."
With his actions in the pool today, Hafnaoui has certainly taken the first step to that goal.