Portugal's Telma Encarnacao scored one goal and set up the other in a 2-0 win over fellow Women's World Cup debutants Vietnam, sending the Southeast Asian side out of the tournament at Waikato Stadium on Thursday.
Portugal are third in Group E with three points and will face the US in their final group game in Auckland while Vietnam, yet to score or pick up a point, take on the Netherlands in Dunedin. Both matches will be played on Tuesday.
The US are level on four points with the Netherlands but top the table on goal difference after the teams drew 1-1 earlier on Thursday.
Portugal coach Francisco Neto made seven changes to the team that lost 1-0 to the Netherlands in their Group E opener and the decision paid off as first-half goals from Encarnacao and Francisca Nazareth earned them a first ever World Cup win.
Neto will be thrilled with Thursday's accomplished performance as Portugal dazzled under the floodlights - a stark contrast to their struggling first display - although the scoreline did not reflect their dominance.
Encarnacao swept Portugal in front after seven minutes with a smart first-time finish from Lucia Alves' cross before turning provider for Nazareth, who fired the ball past goalkeeper Tran Thi Kim Thanh in the 21st minute.
Only 11 places separate the two teams in the world rankings, with Portugal sitting higher at 21, but the contest was one-sided and the Europeans were firmly on top throughout with five attempts on target in the first half alone.
They could not add more gloss to the result, however, as Kim Thanh, who helped restrict holders the United States to three goals in Vietnam's opening defeat, was once again key in ensuring they did not concede more than two.
However, despite Kim Thanh's efforts, Vietnam struggled to create chances and managed only one shot on target in the match when Nguyen Thi Bich Thuy drew a save from Patricia Morais just before the break.
