Defending champions the USA suffered a huge scare against Women's World Cup debutants Portugal before scraping through to the last 16.

The Stars and Stripes are yet to fire at the tournament and, after being held by the Netherlands in their previous match, suffered another frustrating draw that raised questions about their hopes of winning the tournament for an unprecedented third time in a row.

Portugal, who would have caused one of the greatest upsets in the competition's history had they won, hit the post through Ana Capeta in the 91st minute.

In the end the USA were relieved to hear the full-time whistle, the point enough to take them through as runners-up to the Netherlands, who thrashed Vietnam 7-0.

However, the United States were once again far from their best as they struggled to break down a gritty Portugal defence, while keeper Ines Pereira produced two fine saves to deny recalled forward Lynn Williams.

The world's number one side will now face the winners of Group G, which will be decided on Wednesday with Sweden - the last nation to defeat the USA in a 90-minute game at the World Cup - set to finish top unless there is a 10-goal swing.

On a bitterly frustrating night for the four-time world champions in Auckland, midfielder Rose Lavelle was booked and will miss the next game after her second caution of the tournament.