And customers unhappy with yesterday's service can request refunds, Spark announced this afternoon.
Italy play Namibia at 4.45pm, followed by Ireland v Scotland at 7.15pm and England v Tonga at 9.45pm.
Spark's video streaming service cut out for some fans during last night's epic All Blacks-Springboks match, with images of the game flickering, pixelating, blurring and buffering, or losing signal altogether.
The provider was forced to air the remainder of the game free-to-air on TVNZ's channel Duke. But many viewers complained they had not been made aware of the move until late in the game, with some demanding refunds.
Spark this morning apologised for its failings and said it would make a call by 1pm on whether to screen today's games free on TVNZ.
One woman said last night's game was "like watching 80s TV, the quality was so bad", while another said it was like the game had been played on the moon.The streaming issues were "a failure on our part and we apologise to customers for that", Spark Sport spokesman Andrew Pirie told Radio Sport's Jim Kayes this morning.
Spark had been monitoring the quality of the video stream and could see it was starting to fluctuate midway through the first half of the game, Pirie said.
"That wasn't acceptable and so we made an immediate call as quickly as possible and basically decided to start simulcasting the game on TVNZ Duke."
He said the vast majority of customers had continued watching on Spark Sport. "But clearly it wasn't good enough and we apologise for that."
He also acknowledged a banner on the Spark Sport site advising customers of the switch to Duke had not gone up fast enough. Many customers have complained they didn't know it was being screened live on Duke after the Spark issues.
Pirie said technical teams had been working overnight to identify what went wrong. "We believe the issue does lie within the international distribution network. And that's how the video stream passes from our streaming platform...based in the United States through to our New Zealand providers."
While the problem was happening offshore, it was Spark's problem and the company was "owning" the issue.
Asked how embarrassing this was for Spark, he said: "This is not a great experience for us but more importantly it's not a great experience for our customers. These sorts of things are never a good look."
Pirie said Spark was still working through the issue of whether people could get refunds but there was a process for people to register their concerns.
If Spark could not get a "high degree of confidence" that the issues were resolved it would look to simulcast all today's three games on Duke. It would make a call about 1pm today and would continue to make those calls through the tournament.
It was too hard to say how many customers were affected, but he believed it was "a small percentage" at any one time.
Spark Sport operations has screens on the wall showing every device that the game is being streamed to. It was clear that different devices were having problems at different times.
Other customers were experiencing "localised issues" due to their own devices, and Spark had been helping them through that, Pirie said. He said the streaming issue had not been happening in the earlier games.
Spark CEO Jolie Hodson said the company was very disappointed that some New Zealanders did not get "the experience they deserved" during an important match.
"Making a quick decision to give them an alternative means to watch the All Blacks was the right thing to do. We apologise to all impacted customers and we will be working with our partners to rectify what happened and ensure the rest of the tournament goes well."
Spark customers - many of whom had paid between $60-$90 for the privilege of streaming games live through Spark Sport for the six-week tournament - took to social media to complain, with some asking for their money back.
One customer said they had predicted the "absolute shambles" and called for an apology and full refund - as well as making remaining games free to air.
Another said they had watched the game in "glitchy, blurry quality" only to find out it was free on Duke in the last three minutes.
A Dunedin man asked for a refund but Spark only offered him $9 of the original $90 he paid for a Tournament Pass.
Denzell Wiese Christian sent the Herald screenshots from his chat with a helpdesk assistant at Spark Sport.
He had asked for a refund on his Tournament Pass but was only offered 10 per cent back.
He was initially offered help to troubleshoot his device before he made it clear he had found another way to watch the game. The assistant then ended the conversation, the chat desk screenshots show.