The two Six Nations rivals are the favourites to progress from the group and the Irish victory means they have already taken a big stride towards the quarter-finals.

Scotland's hopes of qualification will now likely rest on an awkward final pool encounter with hosts Japan on October 13.

They could not match Ireland's power at the International Stadium Yokohama today with James Ryan barging over for the first try after just seven minutes.

Johnny Sexton converted and the whitewash was crossed again less than ten minutes later when captain Rory Best was driven over.

Sexton missed the conversion this time before Greg Laidlaw's penalty got Scotland on the board for what would be their only points of the match.

Tadhg Furlong powered home for a third Irish try before the break as his side managed to cross with every early excursion into Scottish territory.

Conor Murray slotted the conversion for a 19-3 half-time lead and Andrew Conway added a fourth try, enough for a bonus point, on 56 minutes.

The conversion was missed by Sexton but Jack Carty's penalty later added another three points to the scoreboard.

"We started really well," Best said to ITV Sport.

"We were positive. 

"We wanted to attack.

"We know how good a team they are and we're delighted with that win."

Ireland have climbed to the top of the pool above Japan who opened their home tournament with a bonus point win over Russia.

England, the 2003 winners, recorded an expected comfortable victory over Tonga in Pool C at Sapporo Dome but were not as clinical as they might have hoped to be after their 35-3 success.

Manu Tuilagi scored a pair of tries in the first half and Jamie George and Luke Cowan-Dickie dotted down after the break to secure the bonus point.

Owen Farrell added three penalties and three conversions with the boot as Sonatane Takulua's penalty was all Tonga had to show for their efforts.

"We weren't sharp today but what I really liked was the attitude of our players," said England coach Eddie Jones to BBC Sport.

"That's the second Test in a row we haven't conceded a try and that gives you a real feel of where we're at as a team.

"We lacked a bit of cohesion for some reason today. 

"Maybe that's the dislocated training we've had over the last couple of weeks.

"As coaches we need to look at that but I was so pleased with the players."

England now lead the pool in front of France who beat Argentina without the try bonus yesterday.

The two qualification places are expected to be fought for by the three countries.

Italy opened their Pool B account by defeating Namibia 47-22 at Hanazono Rugby Stadium in Osaka.

They led 21-7 at the break despite the African part-timers taking a shock lead through Damian Stevens' try.

A penalty try drew the Italians level before Tommaso Allan and Tito Tebaldi crossed the whitewash to put their side in command.

They added four more tries after the restart, to comfortably secure the bonus point, as Edoardo Padovani, Carlo Canna, Jake Polledri and Matteo Minozzi all went over.

Allan kicked three conversions and Canna two as early rain made way for sunshine.

Namibia showed spirit as they added further tries through JC Greyling and Chad Plato, while Cliven Loubser dissected the uprights with two conversions and a penalty.

Italy have gone top of the pool but will still struggle to advance as heavyweights New Zealand, the back-to-back defending champions, and South Africa are also in the group.

The All Blacks opened their title defence with victory over the Springboks yesterday.

"The important thing was to win and take the five points," Italy captain Sergio Parisse, who became only the third man to play in five World Cups, said.

"Big congratulations to Namibia as well because they never gave up. 

"They kept playing to the end."

One game is scheduled tomorrow with Wales taking on Georgia in Pool D, at the City of Toyota Stadium.