Ireland scored five tries in a bonus-point win over Russia to go back top of Pool A but the victory was far from convincing.
They will now qualify for a quarter-final should they claim five match points against Samoa in nine days time but serious questions remain about the form of the team, who still looked shook from Saturday’s defeat to Japan.
Whether the knock-out game will be against New Zealand or South Africa depends on how Japan fare against Samoa and Scotland.
FULL TIME: Ireland 35 - 0 Russia.
Ireland: Rob Kearney, Andrew Conway, Garry Ringrose, Bundee Aki, Keith Earls, Jonathan Sexton (captain), Luke McGrath; Jordi Murphy, Peter O'Mahony, Rhys Ruddock, Jean Kleyn, Tadhg Beirne, John Ryan, Niall Scannell, Dave Kilcoyne.
Reserves: Sean Cronin, Andrew Porter, Tadhg Furlong, Iain Henderson, CJ Stander, Joey Carbery, Jack Carty, Jordan Larmour.
Russia: Vasily Artemyev (captain), German Davydov, Igor Galinovskiy, Kirill Golosnitskiy, Denis Simplikevich, Ramil Gaisin, Dmitry Perov; Viktor Gresev, Tagir Gadzhiev, Anton Sychev, Bogdan Fedotko, Andrey Garbuzov, Kirill Gotovtsev, Evgeny Matveev, Andrei Polivalov.
Reserves: Stanislav Selskii, Valery Morozov, Vladimir Podrezov, Andrey Ostrikov, Evgeny Elgin, Sergey Ianiushkin, Roman Khodin, Vladimir Ostroushko.
While Semi Radradra scored two tries and Levani Botia made five conversions, leading previously winless Fiji to a 45-10 rout of Georgia in the World Cup Pool D action.