Munster lock RG Snyman was left to rue South Africa's missed chances as the world champions fell to defeat to Ireland on Saturday night.
The Springboks are now playing catch-up in Pool B and, if Ireland beat Scotland on 7 October, cannot finish ahead of Andy Farrell's side, even if they take care of Tonga in their fourth and final group game.
The 13-8 loss in Stade de France was South Africa's first World Cup defeat in their last nine games, the previous reverse coming in the opening match of the 2019 tournament against New Zealand.
Ireland outscored the Boks 9-3 on turnovers won.
"I think as far as Test matches go, that really was up there," said the 28-year-old lock, who came on in the 47th minute.
"It was a good contest between number one and number two in the world. We probably could have used our opportunities better, so that's what we’ve got to work on.
"I must say, in the 30 Tests I’ve had, that’s definitely up there. It was definitely a physical battle and they really stuck in there.
"[The physicality is] obviously the way we go about things, I just think [taking our] opportunities are the biggest thing to work on.
Snyman made four tackles and ran for 18 metres, making a superb midfield line break before getting hauled down.
On finding himself in open country, he said: "Sometimes when us forwards make various line breaks we never really know what to do with the ball. I should probably get some tips from Damian [de Allende] or somebody like that.
"I don’t really think [Ireland] brought anything different to what we had seen, they just really stuck to their guns.
"I think they were probably the better team because every opportunity they got, they used it.
"They have great guys who can get over the ball, so we definitely expected that, but I don’t think we expected it to that extent."
South Africa were six times in the Irish 22 but averaged only 1.33 points per entry.
"I don't think there was a lack of effort from our side," said the 6ft 7" forward.
"I just think opportunities in their 22, we should have done much better on that. I guess on the night they were a bit better than us.
"We should probably look after the ball a bit better in the 22 and just stick to what we do."
Snyman, who helped Munster to the URC title last season, was up against club team-mates Peter O'Mahony, Tadhg Beirne, Conor Murray and Jack Crowley.
"Yeah, I saw a couple of them. I had the opportunity to swap jerseys with Tadhg Beirne," he added.
Meanwhile, Springboks director of rugby Rassie Erasmus has defended the decision not to add Handre Pollard to the match-day squad after calling the World Cup winning out-half into his panel last weekend. Pollard had been recovering from a calf injury and lined out for Leicester Tigers last weekend.
The three-time champions missed four kicks. Stand-in kickers Manie Libbok and Faf de Klerk missed two apiece and never looked comfortable over the ball.
"You have to see things in perspective. Handre Pollard is not Superman," said the former Munster boss.
"Four weeks ago, he was totally not ready to play rugby. He hasn’t even run full pace four or five weeks ago. He has only played 40 minutes of rugby.
"He can’t just come on the field and do goal-kicking; he must tackle, pass, do kick-offs, sidestep, do hand-offs, clean out at the rucks. People think we didn’t pick Handre Pollard because we didn’t want to. That’s not the case. Handre was injured.
"He has only had 40 minutes of rugby and a week of training with us last week. This week will now be full-on contact where he doesn’t sit out a session. That’s why I said he wasn’t up for selection last week. But we were always going to rotate the squad for the Tonga match so he’s definitely up for selection for this match.
"If you weigh up the different things Manie does… it is like Deon Fourie's lineout throwing. I think he got four lineouts and one not straight, but the scrums went really well. Manie is obviously in a bit of a dip with his goal-kicking.
"He knows it, we know it, the world knows it, everybody keeps on talking about it. When Faf took one kick from 55 metres, he hit the upright and we almost scored from it. Faf is a really good goal-kicker but he is not always going to be on the field.
"Handre is playing this weekend, but let’s see first of all how Handre does the other stuff in the game. Does he get through it on the contact side of things? I am sure he’ll also take some time to find his rhythm with his kicking under pressure.
"The Tonga one will be a great test for him as a yardstick to see where he is before we go - if we go – into those quarter-finals, and who will be on the field. Manie is certainly playing brilliant fly-half rugby at the moment, obviously his goal-kicking is not matching that at this stage."
