Substitute Silvestre Varela headed in a stoppage-time equaliser against the United States to keep Portugal's slim World Cup hopes alive.
The USA were just seconds away from winning their second consecutive game when Cristiano Ronaldo made a perfect cross into the box for Varela to head past goalkeeper Tim Howard and force the 2-2 draw.
Portugal had taken a fifth-minute lead when Manchester United winger Nani punished a poor defensive clearance by Geoff Cameron but the Americans drew level with a long-range strike from Jermaine Jones after the hour mark.
USA captain Clint Dempsey then gave Jurgen Klinsmann's side a 2-1 lead nine minutes from time, but the Portuguese would snatch a vital point in Manaus.
The outcome at the Arena Amazonia leaves the Americans level with their final Group G opponents Germany on four points.
Ghana and Portugal, however, are both three points off the pace before facing one another.
The United States went into the contest looking to win their opening two World Cup games for the first time since the 1930 finals
Klinsmann was without injured striker Jozy Altidore and made just one change to the side that beat Ghana 2-1, with Graham Zusi strengthening the midfield line and Dempsey playing as the lone striker.
Portugal coach Paulo Bento made three alterations to the team that crashed to a heavy defeat to Germany.
Beto replaced injured goalkeeper Rui Patricio, while Ricardo Costa came in for suspended defender Pepe and Miguel Veloso took injured Fabio Coentrao's place in midfield.
The Portuguese dominated early possession and were gifted an early goal.
Veloso's cross into the area was poorly cleared by Cameron and the ball fell into the path of Nani, who slammed the ball past a helpless United States goalkeeper Tim Howard from six yards.
The Americans had their first chance in the 12th minute, Dempsey's 25-yard free-kick going just over the crossbar.
Bento was forced to make his first substitution with Eder replacing the injured Helder Postiga.
Dempsey then twice had the chance to level matters.
Michael Bradley sent his captain through and Dempsey's right-footed shot from eight yards was kept out by Beto.
Then, seconds later, an unmarked Dempsey got behind a corner-kick and lobbed the ball just over the bar.
In the 26th minute, Costa made a vital block on Dempsey's goal-bound attempt.
Bradley then dragged a left-footed shot wide of the far post from outside the area as the Americans got closer.
On the half-hour mark, a fast counter-attack saw Dempsey set up Fabian Johnson on the right.
He found space and blasted a left-footed shot that curled just past the top right corner.
Ronaldo, the recent Ballon d'Or winner, had his first attempt on goal in the 35th minute with his bullet strike going straight into Howard's arms.
Ronaldo then fed Nani on the right of the box and he drilled a right-footed shot that was parried away by Howard.
Before the break, Nani's right-footed effort hit the near post and the rebound fell to Eder.
His effort was on target but Howard, who was falling to his right, managed to raise his left arm and hit the ball over the bar.
Early in the second half, Beto produced a good save to clear Johnson's effort that had been deflected by Veloso.
The Americans should have equalised in the 55th minute when Johnson served up a perfect ball from the right side to Bradley.
The midfielder, with Beto out of position, hit the ball right-footed towards goal but it went straight into Costa, who was on the goal-line.
Klinsmann's side were finally rewarded in the 64th minute when Jones drilled a right-footed shot from outside the area into the lower right corner with Beto rooted to the spot.
Portugal reacted and, in the 66th minute, Howard had to make a great save to parry Meireles' powerful 12-yard shot.
But the Americans soon went in front.
Bradley's attempt was deflected to the left and into the feet of Zusi, who crossed to Dempsey.
The former Fulham star managed to push the ball into the back of the net with his stomach.
But there was further drama to come. Portugal last-ditch attempt to score proved successful with Howard unable to keep out Varela's flying header.