Ireland opened their Rugby World Cup campaign with a bonus-point win as they scored 12 tries to overwhelm Romania in stifling heat in Bordeaux.

They added seven more after the break to record their biggest World Cup win.

Johnny Sexton marked his return with 24 points, including two tries, as he surpassed Ronan O'Gara as Ireland's record World Cup scorer.

Sexton, who eclipsed O'Gara's Six Nations record earlier this year, now sits just nine points adrift of the Munster legend's Ireland Test record of 1,083 points.

The 38-year-old had not played since Ireland's Grand Slam-clinching win against England in March because of injury and suspension.

But he looked sharp on his return as he led the world's number one-ranked team to a routine Pool B win in testing conditions at Stade de Bordeaux.

With their first assignment comfortably negotiated, Ireland face a stiffer challenge against Tonga next Saturday before moving on to the even more daunting tasks of South Africa and Scotland.

Sexton stars as Ireland dominate

Ireland went into Saturday's opener as one of the tournament favourites, having won every Test since topping the world rankings after last year's series win against New Zealand.

After watching potential quarter-final opponents France - who Ireland beat to the Grand Slam in March - issue an ominous statement against the All Blacks on Friday, Andy Farrell's side recorded a big win of their own, albeit against much weaker opposition.

However, what became a comfortable victory started with a blip. Just three minutes in, Romania pounced on Sexton's attempted chip through to Keith Earls, allowing Rupanu to score.

Ireland were never going to panic though and, with Sexton increasingly influential, they stamped their authority on the game with Jamison Gibson-Park, Hugo Keenan and Tadhg Beirne all touching down.

Romania's cause was not helped by full-back Marius Simionescu being sin-binned for obstruction before the outstanding Bundee Aki scored and set one up for Sexton.

Irish fans will have been concerned to see Sexton's reaction after scoring, with the fly-half's wrist caught by Jason Tomane's knee as he was dotting down.

But the playmaker re-emerged for the second half and picked up his second try of the afternoon before going off to a standing ovation 16 minutes from time.

Romania wilt as Ireland run up record

While Romania caused Ireland some problems in the opening exchanges, the 19th-ranked team in the world wilted badly in the second half as Ireland amassed their record World Cup haul.

Ireland will pick holes in their performance, notably the line-out, but the quality of their attack shone through as they scored tries for fun in the Bordeaux sun.

Sexton added his second - his 17th Test try - while Rob Herring, Peter O'Mahony with two, Joe McCarthy, Aki and Beirne completed Romania's misery.

While Sexton notched his most points in a match for Ireland, there was an impressive cameo from his fly-half understudy Jack Crowley, who came off the bench to kick four conversions.

With a record win in the bag, Ireland will quickly switch focus to next week's match in Nantes, knowing Saturday's win in Bordeaux was merely the first box ticked on what they hope is a path to a first World Cup title.

Analysis

Former Ireland fly-half Tony Ward on BBC Radio Ulster: "There are no injuries we can see, the bench has been emptied, they've all had a run out, Sexton has fitted back in, McCarthy has had a tremendous first start and has looked really impressive and Bundee Aki was outstanding throughout."

Former Ireland wing Tommy Bowe on BBC Radio 5 Live: "Credit to Ireland for keeping on playing. To make it to 80 points in your opening match of the World Cup is a statement. I'm very impressed and can't wait to see how far Ireland can go in this tournament."

Teams

Ireland: Keenan; Earls, Ringrose, Aki, Lowe; Sexton (capt), Gibson-Park; Doris, O'Mahony, Beirne; Ryan, McCarthy; Furlong, Herring, Porter.

Replacements: Kelleher, Loughman, O'Toole, Henderson, Van der Flier, Murray, Crowley, Hansen.

Romania: Simionescu; Onutu, Tangimana, Tomane, Manumua; Vaovasa, Rupanu; Chirica (capt), Neculau, Rosu; Iancu, Motoc; Gordas, Cojocaru, Hartig.

Replacements: Savin, Gajion, Iftimiciuc, Ser, Conache, Boldor, Gontineac.

Not used: Bardasu.

Sin bin: Marius Simionescu (32)

Referee: Nika Amashukeli (GEO)