Angel Cabrera said he had achieved the impossible after pipping Tiger Woods and Jim Furyk to the US Open title at a brutal Oakmont Country Club.
Cabrera has previously had six top-10 finishes in the majors
The 37-year-old Argentine beat the more illustrious American pair by one shot to clinch his maiden major.
"I never thought this was possible," Cabrera said. "It's a great moment for me, I can't believe it.
"Probably tomorrow, when I wake up with this trophy beside me in my bed, I will realise that I have won the US Open."
Cabrera became only the second South American to win a major after compatriot Roberto de Vicenzo clinched the Open at Hoylake in 1967.
Vicenzo famously went close again at the Masters the following year but signed for the wrong score, keeping him out of a play-off.
Cabrera added: "It is very difficult to describe at the moment. I watched all the majors on TV when I was a kid. I never thought I would be here at this moment."
Some players have psychologists, some have sportologists - I smoke
The big-hitting star from Cordoba, a three-time European Tour winner, led after the second round but has a reputation for losing his concentration and was not expected to maintain the challenge.
But as his rivals faltered on a tense final day, Cabrera stuck to his natural attacking game and stretched to a three-shot lead after 15 holes before handing shots back at 16 and 17 to rejoin Furyk on five over.
But Furyk, the 2003 champion, bogeyed 17 and Cabrera's par up the last set the clubhouse target.
"Teeing off on 18 was the most difficult moment and tee shot of the day," said Cabrera, the only player in the field to post two sub-par rounds.
Cabrera held off former US Open winners Furyk and Woods
"There was a lot of pressure at that time and I had to put the ball in the fairway and make a four and sit and wait.
"I was definitely feeling nervous, but I assumed that this is the same sensation everybody was having in my place."
To stay calm Cabrera, nicknamed "El Pato" - the duck - for his waddling gait, puffed on cigarettes between shots.
"Some players have psychologists, some have sportologists - I smoke," he said.
Furyk, playing behind, was unable to secure a closing birdie to rejoin him and Woods's par on 17 left him also needing to birdie the 18th to force an 18-hole play-off on Monday.
But the 12-time major winner, who has never won one of the big prizes coming from behind on the final day, could only manage par and Cabrera, who began as a caddie at the age of 10, was champion.
This is going to be something to be remembered in Latin America, not only in Argentina
"I wasn't able to finish elementary school and I had to work as a caddie to put some food on the table, so that's why probably these moments are enjoyed even more than the common things," he said.
As a youngster Cabrera was noticed by fellow Cordoban and Argentine golf great Eduardo Romero, who helped him financially before he qualified for the European Tour in 1995 after four attempts.
Cabrera gradually worked his way up the European Tour rankings winning the 2002 Benson and Hedges International and the 2005 PGA Championship.
He also came close to winning the Open at Carnoustie in 1999 and has three top-10s in the Masters. Last year he tied for eighth at Augusta and he tied for seventh at the US Open in 2001.
"I have been looking forward to winning a major. I came very close at the British Open, close at Augusta, so I am definitely enjoying this moment," said Cabrera, who collected $1.225 million for his win.
"This is going to be something to be remembered in Latin America, not only in Argentina."