Sophia Smith struck twice and Lindsay Horan grabbed the other as the US opened their Group E account with three points at Eden Park in Auckland.

The US, seeking a third straight World Cup crown and fifth overall, took the lead on 14 minutes when Smith fired past Tran Thi Kim Than.

The Vietnamese goalkeeper saved an Alex Morgan penalty just before the break only for Smith to net again in first-half stoppage time.

Smith then turned provider, setting up Horan for the US’ third on the 77th minute.

"We want to win every match, so it’s one down and now we move on to the next," said US coach Vlatko Andonovski.

"We created a lot of opportunities and wanted to score more goals, but it is what it is.

"Hopefully we can improve on that and bring some of the good things we did today when we play The Netherlands."

Another World Cup winner in Japan also got their campaign off to a flying start as the 2011 champions crushed Zambia 5-0 at the Waikato Stadium in Hamilton.

It was a one-sided Group C encounter as Japan dominated, and they thought they had opened the scoring only for Mina Tanaka’s strike to be ruled out for offside.

Japan’s persistence paid off on the 43rd minute when Hinata Miyazawa got on the end of Aoba Fujina’s cross to score.

After having another goal chalked off for offside, Tanaka finally got on the scoresheet when she netted on 55 minutes.

Miyazawa scored her second before Jun Endo added a fourth for Japan.

Zambia’s misery was compounded with the sending off of goalkeeper Catherine Musonda following a second bookable offence for taking down Riko Ueki in the box.

Ueki saw her penalty saved by Eunice Sakala only for replays to show that the reserve goalkeeper had come off her line.

The Japanese player made no mistake when she was presented with the retake to complete the rout for her side.

Reigning European champions England were forced to work hard to beat Haiti 1-0 in their opening Group D clash at Brisbane Stadium.

Georgia Stanway scored the only goal on the half-hour mark after converting from the spot at the second time of asking.

The England striker saw her initial attempt saved by Kerly Theus before being presented with another opportunity which she duly dispatched after the Haiti goalkeeper was ruled to have strayed off her line.

The other Group D clash also ended 1-0 with Denmark securing a dramatic win over China at the Perth Rectangular Stadium.

A match that featured few chances appeared to be heading for a goalless draw before Amalie Vangsgaard headed in a corner in the 89th minute to seal victory for Denmark.

"I've waited a long time for the first international goal, so I must have saved it for the best time," said Vangsgaard.

"It's super important that we got off to a good start to the World Cup."

Competition is due to continue tomorrow with Sweden facing South Africa in Group G, The Netherlands tackling Portugal in Group E and France coming up against Jamaica in Group F.