After 36 minutes the unfancied Americans were leading 3-0 against one of the world's best teams.
John O'Brien and Brian McBride were the American heroes, scoring before and after an own-goal by Portugal's Jorge Costa. The United States' three-goal lead owed as much to their endeavour as to a disastrous goalkeeping display by Vitor Baia.
Beto reduced the deficit just before the interval and an another own-goal, this time by American Jeff Agoos, midway through the second half paved the way for a Portuguese comeback.
But the Americans survived the onslaught that followed to send shockwaves through the footballing world with a brilliant win.
The game got off to an explosive start, with O'Brien giving the United States a shock lead on four minutes. From an Earnie Stewart corner, McBride thundered a powerful header straight at Baia. The Portugal keeper could only parry the ball to O'Brien, who sent a rasping shot into the back of the net.
A stunned Portugal looked a pale shadow of the team which had topped their qualifying group so impressively. Defensively they were inept and lacked any kind of organisation. Fifa's World Player of the Year Luis Figo could only look on in despair.
Much of Portugal's uncertainty stemmed from Baia, whose display in the first half will linger long in the memory because of its sheer haplessness. His inability to hold onto the ball or inspire any confidence in his defenders suggested there would be more goals in the game and so it proved.
The United States deservedly extended their lead with half-an-hour gone, albeit rather fortuitously. Costa, given a second chance to clear after his initial error, understandably opted against a back-pass to Baia, who had strayed off his line.
But Costa was dispossessed by Landon Donovan, whose quick strike deflected wickedly off the defender and beyond the reach of Baia. Donovan looked embarrassed, while Baia could not believe he had been beaten again - but it would not be the last time.
An excellent cross from Stewart drifted over Baia and unmarked McBride headed in the United States' third to the delight of Arena and his coaching staff.
The ignominy of a possible defeat to supposedly vastly inferior opponents sparked the Portuguese into action and they pulled one back before half-time. The United States defence failed to deal with a Figo corner and Beto blasted the ball past Brad Friedel at the second attempt.
After the break, Portugal launched wave after wave of attacks in search of another goal. It came on 71 minutes when Agoos sliced the ball past a helpless Friedel following a cross from Pauleta wide on the left.
The pressure from Portugal was incessant after the second goal, but America held out valiantly to cause one of the biggest World Cup shocks ever.
USA
Friedel, Mastroeni, Sanneh, Pope (Llamosa 80), Agoos, O'Brien, Hejduk, Beasley, McBride, Donovan (Moore 75), Stewart (Jones 45).
Goals: O'Brien 4, Costa 29 og, McBride 36.
Portugal
Baia, Costa (Andrade 73), Couto, Beto, Jorge (Bento 69), Rui Costa (Nuno Gomes 79), Petit, Sergio Conceicao, Figo, Pauleta, Pinto.
Goals: Beto 40, Agoos 71 og.
Attendance: 37,306 |