With the sun shining in the Welsh capital, the British women’s team – making their first-ever appearance in the Games – enjoyed a 1-0 win over their rivals, with Steph Houghton breaking the deadlock after 63 minutes, curling a 25-yard free-kick over the wall and past New Zealand goalkeeper Jenny Bindon.
Houghton was delighted that her effort turned out to be the winning goal.
"It was something special and I'm sure my family are really proud,” she said. “I don't think it will sink in for a while. I'm just glad it got us the win."
British captain Casey Stoney, meanwhile, had plenty of praise for the crowd in the Millennium Stadium.
“The atmosphere was fantastic,” she said. “I've never experienced anything like it before.”
In the day’s other matches, 2011 World Cup winners Japan took on Canada in Coventry (2:1) and Beijing 2008 gold medallists USA faced France in Glasgow (4:2).
Cameroon and Brazil also played at the Millennium Stadium, while Sweden and South Africa took on each other in Coventry, and Colombia and DPR Korea took to the pitch in Glasgow.
With the opening round of matches completed, attention turns to the other group stage clashes. Great Britain and New Zealand will now take on Cameroon and Brazil in Group E, the USA and France will face Columbia and DPR Korea in Group G, and Japan and Canada are matched with Sweden and South Africa in Group F.
The three group winners and runners-up will qualify for the knockout stages, where they will be joined by the two best third-ranked teams.
The gold-medal match will take place at Wembley Stadium on 9 August.