The Ireland Under-20s' defensive deficiencies were laid bare again as Scotland ran in six converted tries in a 45-29 World Rugby U-20 Championship play-off win in Perpignan this afternoon.

A pockmarked performance from Noel McNamara's young side, who led 14-3 early on, leaves them needing to defeat Japan in Sunday's 11th-12th place play-off in order to save Ireland from dropping down to the second-tier World Rugby U-20 Trophy tournament for next season.

Harry Byrne nipped over for a 10th-minute opening try and grubbered through to set up Peter Sylvester's first try at this level, but the first half unravelled for Ireland as tries from Finlay Richardson (2) and Logan Trotter, coupled with Hugh O'Sullivan's sin-binning for a no-arms tackle, handed Scotland a 24-17 interval lead.

Third quarter touchdowns from replacement Guy Graham and Kyle Rowe had the Scots out of sight, and while tries from Tommy O'Brien and replacement Jack Daly sandwiched a Devante Onojaife effort, they were of little consolation to Ireland who remain winless after four rounds of the tournament, with an average of 31 points and four-and-a-half tries conceded per game.

The first quarter had looked encouraging from an Irish point of view at Stade Aimé-Giral. Jack Dunne's high tackle allowed Charlie Chapman to boot Scotland in front, but a bout of forward pressure set up out-half Byrne to take a hard line and crash over past Rowe, just to the left of the posts.

Byrne converted his second try of the tournament and it was his brilliantly-weighted grubber off the outside of right boot, in behind a flat Scottish defence, which created Sylvester's 21st-minute score. Byrne added the extras to put 11 points between the sides, a really solid foundation for the win-starved Ireland U-20s.

Number 8 Onojaife's turnover at the breakdown set Scotland on their way to a quick-fire response, as influential tighthead Richardson rumbled over after initially good defence from Ireland. Some impressive continuity and support play wore down the Irish rearguard for Scotland's second try in the 32nd minute as Richardson completed his brace, jinking over from close range for a seven-pointer.

The match officials spotted scrum half O'Sullivan's no-arms tackle on hooker Robbie Smith in the build-up, leaving Ireland down to 14 men. Chapman kept up his 100% kicking form when converting Trotter's 37th-minute try, with Ireland being drawn in by a maul and space was created out wide for the winger to go over.

Still, a Byrne penalty on the stroke of half-time gave 14-man Ireland a timely boost with just seven points separating the sides as they headed for the dressing rooms. The next score was vital and Bryan Redpath's Scottish outfit made sure they got it through the strong-running Graham, who exposed some lacklustre defending in the 48th minute with the returning O'Sullivan and Michael Silvester particularly guilty.

Number 10 Byrne tried to lift Ireland in attack, probing with a dangerous cross-field kick, but Scotland were growing in confidence and another multi-phase surge downfield delivered a classy team try finished off by winger Rowe - all coming from Dan Sheehan's overthrown lineout and a weaving run by Trotter past four defenders.

UCD clubman O'Brien, who was switched to the left wing today, stood out for his work-rate in defence, although his opportunities in attack were extremely limited. Entering the closing quarter, Ireland were finally able to exert some pressure in attack with replacement prop Bryan O'Connor just held up, and a blindside attack from a scrum ending with O'Brien diving over in the corner for a deserved try.

The match officials' obligation to look at a potential incident of foul play saw replacement Conor Dean's conversion attempt ruled out, but he coolly nailed his second kick from out wide to reduce the arrears to 38-24. Onojaife slammed the door shut with a 68th minute try, the subsequent sin-binning of Ireland captain Caelan Doris adding to their woes.

His team-mates did at least show their resilience in the closing stages, with recent debutant Daly notching a hard-earned 72nd-minute try but they were unable to take advantage of Rowe's subsequent sin-binning and 16 points remained the margin. Doris summed up the squad's disappointment afterwards, highlighting the defence, discipline and lineout as areas they need to quickly improve on.

We played Scotland in the Six Nations, played them in a warm-up game and again today. In the first two we came out on top, but it's narrow margins at this level and we knew it was going to be another very close encounter," he said. "Unfortunately for us, they came out on top today.

"We had problems in the lineout. I think it was just miscommunication, missed lifts at times. Just inaccuracies and that gave them entry into the game along with indiscipline. Our discipline, and my discipline, wasn't good enough at times and that allowed them to get territory, and off that they got their maul going and scored tries.

"Fixing the defence, I think it comes back to our hold-fold decisions, working hard early, getting into place early, and then just the one-on-one tackles as well. Just getting our entry right because we missed too many of them today."

Scorers: Ireland: Tries: Harry Byrne, Peter Sylvester, Tommy O'Brien, Jack Daly; Cons: Harry Byrne 2, Conor Dean; Pen: Harry Byrne

Scotland: Tries: Finlay Richardson 2, Logan Trotter, Guy Graham, Kyle Rowe, Devante Onojaife; Cons: Charlie Chapman 6; Pen: Charlie Chapman

IRELAND U-20: Michael Silvester (Dublin University/Leinster); James Hume (Banbridge/Ulster), Sean O'Brien (Clontarf/Leinster), Peter Sylvester (UCC/Munster), Tommy O'Brien (UCD/Leinster); Harry Byrne (UCD/Leinster), Hugh O'Sullivan (Clontarf/Leinster); Jordan Duggan (Naas/Leinster), Diarmuid Barron (Garryowen/Munster), Joe Byrne (Dublin University/Leinster), Matthew Dalton (Malone/Ulster), Jack Dunne (Dublin University/Leinster), Joe Dunleavy (Malone/Ulster), Matthew Agnew (Ballymena/Ulster), Caelan Doris (St. Mary's College/Leinster) (capt).

Replacements used: Dan Sheehan (Dublin University/Leinster) for Barron, Bryan O'Connor (UCC/Munster) for Duggan (both 49 mins), Duggan for J Byrne (52), Charlie Ryan (UCD/Leinster) for Dalton, Conor Dean (St. Mary's College/Leinster) for H Byrne (both 57), Jack Daly (Garryowen/Munster) for Agnew (59), Jonny Stewart (Queen's University/Ulster) for O'Sullivan (62), Jakub Wojtkowicz (Sligo/Connacht) for Duggan (73), Tom Roche (Lansdowne/Leinster) for Silvester (76).

SCOTLAND U-20: Paddy Dewhirst (Ayr); Logan Trotter (Stirling County), Cameron Hutchison (Currie Chieftains), Stafford McDowall (Ayr) (capt), Kyle Rowe (Glasgow Hawks); Callum McLelland (Edinburgh), Charlie Chapman (Gloucester); Sam Grahamslaw (Leicester Tigers), Robbie Smith (Ayr), Finlay Richardson (Edinburgh Accies), Jamie Hodgson (Watsonians), Marshall Sykes (St. Joseph's College), Martin Hughes (Heriot's), Rory Darge (Melrose), Devante Onojaife (Northampton Saints).

Replacements used: Guy Graham (Newcastle Falcons) for Hughes (11 mins), Finlay Scott (Jed-Forest) for Smith, Murphy Walker (Strathallan School) for Grahamslaw (both 52), Ross Dunbar (Boroughmuir) for Richardson, Ross Thompson (Glasgow Hawks) for McLelland (both 73), Charlie Jupp (Heriot's) for Hodgson (78). Not used: Charlie Gowling (Stade Francais), Fraser Strachan (Northampton Saints).

Referee: Egon Seconds (South Africa)