Match report and highlights: Ireland 44-10 Romania
Keith Earls and Tommy Bowe scored two tries each as Ireland cruised to the top of Pool D with a bonus-point victory over Romania.
In front of 89,267 fans at Wembley, a record Rugby World Cup attendance, Ireland made light of 12 changes to their starting XV to record a comfortable 44-10 win.
Earls and Bowe notched a try in each half before substitute Rob Kearney and Chris Henry added two more late on, with Ian Madigan kicking 14 points in the victory.
Romania managed a consolation score through Ovidiu Tonita but it is Ireland who move into pole position to make the quarter-finals, with pivotal games against Italy next Sunday and France still to come.
Ireland were expected to claim another convincing World Cup victory against Romania and climb back to the top of Pool D.
With pivotal tests against Italy and France still to come, head coach Joe Schmidt made 12 changes for the clash at Wembley, which included a rest for star fly-half Johnny Sexton.
Romania, ranked 17th in the world, were without their sole try-scorer from the opening defeat to France, as Valentin Ursache served a one-match suspension.
Ireland wasted no time in asserting their superiority as Tommy Bowe and Simon Zebo enjoyed early breaks before Ian Madigan capitalised on a Romania offside to slot home the game's first penalty.
Schmidt's team had dominated the opening stages but, with 10 minutes gone, Romania restored parity when scrum-half Valentin Calafeteanu kicked through the posts after Jared Payne failed to roll away from a ruck.
The whole stadium were on their feet moments later, as Ireland thought they had a sensational try when Zebo raced down the wing, kicked through, before collecting and diving over in the corner.
It was a brilliant piece of skill from Zebo but TMO showed the winger to have planted his left foot in touch and the score was ruled out.
Ireland, however, would not be thwarted for long as Madigan kicked another penalty before Bowe scuttled into the corner, this time squeezing just inside the line, for the opening try and Madigan added the extras to give his side a 13-3 lead after 21 minutes.
Keith Earls had taken an excellent high catch in the build-up to Bowe's score and in the 29th minute, he went from provider to scorer, latching on to a long Zebo pass and speeding straight into the corner for a second Ireland try and his sixth at World Cups.
Madigan struck the post with his conversion from out wide but the Irish were in control and the only surprise was they were unable to extend their 15-point advantage before half-time.
Less than four minutes into the second period, however, Ireland crossed the whitewash again as an agricultural boot up the field from Cian Healy earned a well-placed line-out before Earls gathered a neat grubber from Eoin Reddan to cruise over.
The try was Earls' seventh at World Cups, making him Ireland's joint top-scorer with Brian O'Driscoll in the tournament's history, but the number 11 left the field soon after with what appeared to be a head injury.
Madigan kicked the conversion but while Earls returned to action shortly before the hour mark, the all-important fourth try continued to elude the Irish, who were still dominating territory and possession.
Romania, run ragged, began to lose their discipline as first Florin Ionita was fortunate to escape punishment for tackling in the air and then centre Csaba Gal was shown the yellow card for a cynical intervention at a ruck.
With one man less, the floodgates opened as Ireland finally secured the bonus-point with two tries in four minutes.
Reddan flung the ball out to Bowe, who brushed off Ionut Botezatu to roll into the corner, and moments later Zebo's pop inside freed substitute Rob Kearney to crash through for try number five.
Madigan added the first but not the second conversion as Ireland led 37-3 with 10 minutes to play.
They were not finished yet as Chris Henry touched down his fourth international try after a driving maul but it was Romania who had the last word, as Ovidiu Tonita crashed over from close range for a consolation score.
Florin Vlaicu converted to reduce the deficit but it was too little too late as Ireland completed a convincing victory.