TOKYO — An 18-year-old Tunisian managed to pull off a surprise upset in the 400-meter freestyle swimming event, finished ahead of Australia's Jack McLoughlin and US swimmer Kieran Smith.

Ahmed Hafnaoui erupted in jubilation when he realized he won in the extremely tight race, pumping his fists and placing both hands on his brow as he took in the victory.

He seemed genuinely shocked at the result: "I just can't accept that — it is too incredible."

"I dedicate (the gold) to all my family, my mum, my dad, my sisters, I wish they are proud of me."

His gold medal is only the fifth won by a Tunisian athlete at the Olympics, but their third in swimming.

Hafnaoui came into the race with the slowest qualifying time of the eight swimmers — but he touched the wall first.

When asked how he kept his lead, he simply said: "I don't know, I just put my hand in the water, that's it." The swimmer seemed at a loss for words. Shaking his head, he said, "it's a dream that became true."

Just three years ago, Hafnaoui was competing in the Youth Olympic Games, placing 8th in this same event in Buenos Aires.

The last swimming Olympic medal for Tunisia was in 2012 at the London Games, when Oussama Mellouli won gold in the 10 km marathon. — Agencies