Two-time champions South Africa recorded one of their biggest Rugby World Cup wins on Saturday when they routed a porous Namibia 57-3 to move towards the quarter-finals.

Five tries in the first half and another four in the second swept Namibia aside as the Springboks briefly threatened to eclipse the 87-0 win, the heaviest they have recorded at World Cups, over the Welwitschias in 2011.

After Japan’s sensational 19-12 victory over Ireland earlier on Saturday, any hopes of another upset were quickly snuffed out at a packed City of Toyota Stadium as South Africa attacked relentlessly from the outset.

The Springboks next face Italy in a match that will go a long way to deciding who qualifies from Pool B, which also contains defending champions New Zealand. “We will build from this and now we’ve got this big Italy game which probably will determine if we go through to the quarter-finals or not,” said Springbok coach Rassie Erasmus. “And I think this game will give us a nice springboard to go into that game.”

Namibia kept South Africa scoreless for just nine minutes at the start of the game before three catch-and-drive tries in the space of seven minutes put the outcome beyond doubt.

Hooker Bongi Mbonambi barged over for a routine score before Francois Louw went over in similar circumstances, following RG Snyman’s slick back-of-the-hand offload in the build-up.

By the time Mbonambi had pushed over for his second try, Namibia’s Adriaan Booysen was in the sin-bin for a deliberate knock-on and the Welwitschias were yet to get out of their half apart from re-starts.

Cliven Loubser put Namibia on the board when their first attack yielded a penalty, but they fell further behind when scrum-half Herschel Jantjies’ sharp pass found Warrick Gelant who put Makazole Mapimpi over in the corner.

S’busiso Nkosi and Gelant’s back-to-back offloads then left Namibia scrambling before long-time hooker Schalk Brits, playing at number eight, fed Lukhanyo Am for South Africa’s fifth try on the stroke of half-time for a 31-3 lead.

Am’s mazy run set up Gelant for South Africa’s sixth try, before Brits’ no-look pass fed Mapimpi for their seventh and Siya Kolisi, replacing Kwagga Smith, ran in the eighth for a 50-3 lead just short of the hour-mark.

Johannes Coetzee became Namibia’s second player in the sin-bin for an off-the-ball challenge on Brits – who bustled his way across the tryline from the ensuing lineout on 64 minutes. It was to be the final score for South Africa, who lost their Pool C opener 23-13 against New Zealand and move on to face Italy next Friday.

“I think obviously when you lose a game like the previous game, you want to get some momentum back,” said Erasmus. “We saw today what Japan did to Ireland... We’ll be really careful.”