Samoa maintained their slim chances by flattening Pacific island rivals Fiji. Meanwhile Argentina, who finished third at the last World Cup four years ago, was seven minutes away from elimination after a grinding battle in the Wellington rain.
That was until replacement winger Lucas Gonzalez Amorosino produced a piece of magic to scythe through the Scottish defense for the game's only try, which captain Felipe Contepomi nervelessly converted for a 13-12 victory.
Scotland, playing with controlled aggression as Argentina struggled to deal with an injury pile-up, had built a 12-6 lead with penalties from Chris Paterson and Ruaridh Jackson and drop goals by Jackson and his replacement Dan Parks.
Neither side had come close to a try in testing conditions but Amorosino, man of the match in their last game against Romania, caught the Scottish defense cold with a superb slaloming run to turn the match.
The result leaves England top of Pool B on 14 points, with Argentina and Scotland both on 10.
With Argentina likely to beat Georgia in their final game, Scotland would have to beat England, either with a bonus point or preventing England getting one, to maintain their proud record of reaching at least the quarterfinals of every World Cup.
The pool winners are likely to face France while the runners-up will play New Zealand.
"It was an amazing game," said Amorosino. "We know we need to play until the last minute — it's a World Cup, you have to stay focused." Scotland coach Andy Robinson said his players were absolutely devastated.
"It's one lapse, it's 30 seconds that has cost them a test match. You have to finish off sides like Argentina, but credit to them, they were under a lot of pressure." There was no such pressure on Ireland, who backed up their upset win over Australia last week with a 62-12 thrashing of Russia — though the tournament debutants did score two tries in Rotorua.
Keith Earls crossed twice for Ireland while flyhalf O'Gara gave a masterclass, kicking seven from eight goal attempts and marshaling a backline featuring several squad players.
"A few guys got an opportunity this week to back up the performances of the weekend," said Ireland stand-in captain Leo Cullen. "It was important to continue the momentum." For Samoa to reach the last eight for the first time since 1995 they almost certainly need to beat Pool D leaders South Africa next week — something they have come nowhere near threatening in six previous meetings.
Their World Cup hopes were effectively derailed by last week's defeat by Wales but they bounced back with a 27-7 victory over Fiji, who needs a miracle combination of results to match their 2007 achievement of reaching the quarterfinals.
Samoa led 12-0 at halftime before a sellout crowd of 60,000 Eden Park crowd as the city's Polynesians turned out in force, with three penalties and a drop goal by flyhalf Tusi Pisi.
Scrumhalf Kahn Fotuali'i claimed the first try after an hour and though flanker Netani Edward Talei finally crossed for Fiji, their slim hopes were crushed almost immediately when number eight George Stowers capped a superb individual performance with their second try.
"This game is all about pressure and if we kept on the pressure (we knew) we'd get some points," said Samoa captain Mahonri Schwalger "If you want to win a test like this against a strong side like Fiji you have to make sure you get your points when you get down in their 22." Fiji's experienced flyhalf Nicky Little said his team had let down their fans and even apologized to his opponents.
"I feel sorry for Samoa. We did not put up a good enough fight so apologies for that," he said. "I do not think we fired a shot."
