The Irish, making their first World Cup appearance for eight years, were 42-14 winners over Japan, while South Africa beat a Brazil side making their tournament debut 66-6.
A good-sized crowd turned out as the sun shone over Franklin's Gardens as the World Cup hit Northampton, with the double header being played at the home of the Saints.
The matches were the first of six to be played at the Gardens, with the next pencilled in for Saturday (Aug 30) when hosts England are in town to take on Samoa (ko 5pm).
Ireland then return to Northampton next Sunday to take on Spain (ko midday), before another double header on Sunday, September 7 sees Italy take on Brazil (2pm) and France host South Africa (4.45pm).
The Irish ran in six tries as they got the better of a spirited Japan side, and head coach Scott Bemand was happy with the result.
“Credit to Japan, they don’t give up," said Bemand. "We said they’d be disciplined and well-organised and would present a formidable challenge.
“It was really pleasing to get a bonus point before halftime. You’re acclimatising to tournament rugby, finding the rhythm, so it was important to get our game going and get on the board.
"There’s always bits to work at. A far from perfect performance but stacked with bits to be happy with.”
Japan head coach Lesley McKenzie fele her side's clash with the Irish at the Gardens had been the 'game of the round'.
“You can’t fault the team on the effort, especially the response in the second half to a first half that wasn’t where we wanted it to be," said McKenzie.
“I would really have enjoyed that game had I not been coaching it. What a game, I reckon that was the game of the round."
South Africa scored 10 tries in their win over Brazil, with Aseza Hele running in a hat-trick, but one of the biggest cheers of the day was reserved for Raquel Kochhann, whose 10th-minute penalty gave Brazil their first points in Rugby World Cup history.
South Africa head coach Swys de Bruin was emotional in victory, and said: “I know where these girls come from, I know their stories, they deserve this.
"It shows South Africa what they can do. I feel blessed. For a year with this group, you realise they played way above. It was fantastic to see, they made us proud."
Brazil head coach Emiliano Caffera was proud of his team after they battled away with just 29 per cent of possession and 25 per cent of territory.
“It’s difficult to be always defending," said Caffera. "They start getting tired. They were always running but it’s difficult, they didn’t have a lot of the ball.
“They know the level now and I think we will have a better game next time.”

1. Warm welcome
Captain Eshyllen Coimbra Cardoso of Brazil holds a Upepe as she leads the team out prior to the Women's Rugby World Cup 2025 Pool D match between South Africa and Brazil at Franklin's Gardens in Northampton (Photo by David Rogers/Getty Images) Photo: David Rogers

2. Seven up!
Libbie Janse van Rensburg of South Africa dives over to score her team's seventh try during the Women's Rugby World Cup 2025 Pool D match between South Africa and Brazil at Franklin's Gardens in Northampton (Photo by David Rogers/Getty Images) Photo: David Rogers

3. Joy and pain...
South Africa's fly half Libbie Janse van Rensburg (second from right) celebrates a try during the Women's Rugby World Cup pool D match between South Africa and Brazil at Franklin's Gardens in Northampton (Photo by PAUL ELLIS/AFP via Getty Images) Photo: PAUL ELLIS

4. Standing out from the crowd!
Raquel Kochhann of Brazil looks on during the Women's Rugby World Cup 2025 Pool D match between South Africa and Brazil at Franklin's Gardens (Photo by David Rogers/Getty Images) Photo: David Rogers

