Replacement out-half Freddie Burns scored two second half tries to decide this Rosario clash, the second a late intercept effort as Ireland desperately tried to get back in touch.
Having led 16-11 at half-time, England kept the scoreboard ticking over and made Ireland work overtime in defence without showing much penetration.
James McKinney landed his third penalty of the afternoon to keep the Six Nations champions in the hunt at 19-14, but England stretched their advantage to 12 points when Burns spotted a mismatch close to the Irish posts and ghosted over for his first try.
Full-back Tom Homer, who kicked 21 points in all, added the conversion and another penalty before Burns intercepted a pass from Noel Reid as Ireland attacked near the English 22 and darted clear for the killer score which Homer converted.
It gave a flattering gloss to the scoreline as Ireland deserved to be closer, and they showed their mettle when hitting back, just four minutes later, with a well-taken try by replacement centre Eoin Griffin.
But England were the superior outfit on the day, gaining revenge for a 25-10 Six Nations loss to the Irish in Gloucester.
The result, coming on the back of last Sunday's 25-22 defeat to France, means Allen Clarke's youngsters are out of contention for a semi-final place.
Clarke had made three changes to the Ireland side that lost to the French, with Brendan Macken and Noel Reid forming a new centre partnership, Nevin Spence moving to the right wing and Brian Hayes included at the expense of Ben Marshall in the second row.
England boss Mark Mapletoft made a total of ten changes to his starting line-up, following their opening 48-22 victory over hosts Argentina. Runners-up in the last two Junior World Championships, the pressure is on for England to go one better.
They did not look like title contenders in the first half, and neither did Ireland as handling errors and nerves blighted the game. There was a blanket of tension over the pitch, both sides obviously determined to give no quarter.
Ireland got off to a positive start as English loosehead prop Lee Imiolek infringed at a third-minute scrum and McKinney landed the resulting kick from left of the posts.
But a break from big centre Tom Casson showed the power England possess and when Spence was pinged for not releasing after the tackle, Homer kicked them level.
The place-kickers landed their second shots at the posts soon after, with McKinney's effort coming after a solid Irish scrum and clever inside switch between UCD duo John Cooney and Reid.
Disappointingly, Ireland invited England onto them in the lead-up to their first try. Hooker Niall Annett was ruled to be ahead of the kicker as Reid tried to thump downfield. That set up an English scrum in the 18th minute and after a forceful Casson run, flanker Jamie Gibson did well to break Dominic Ryan's tackle and twist over under pressure from Reid.
Homer converted and then punished Jack O'Connell for a scrum infringement as England moved 16-6 ahead.
Ireland had been feeding off scraps, particularly their outside backs, and they showed their counter attacking ability in the 33rd minute when winger Simon Zebo burst into the English 22.
The Munster winger took an inviting pass from Macken and fended off the first tackler, setting up possession five metres from the whitewash, but the second phase saw Macken knock on in midfield.
The attack showed what Ireland could do and they were beginning to see more of the ball as the first half came to a close. A good tackle by Spence on Rory Clegg forced a penalty and Ireland set up a last-gasp attack.
In injury-time, Ireland moved the ball wide off a set scrum, McKinney and Macken fed Zebo the burst and the winger took contact before passing for the looping Macken to send full-back Andrew Conway over in the left corner.
It was simple but very effective and a score that was as much about the hard graft of Rhys Ruddock and his forward colleagues in the preceding minutes. McKinney failed to convert from the touchline, leaving Ireland just five points in arrears at the break.
Griffin and lock Ben Marshall were introduced on the resumption and Ireland continued to grow in confidence. They defended an early English raid before the eager Spence was called back for a forward pass after some neat link-up play.
England, however, benefited from some good continuity, using their forwards to gain ground through the middle and set up Homer's fourth successful penalty - this time from long range.
A late tackle by Casson on McKinney allowed the young Ulster out-half close the gap to 19-14, firing over from 28 metres out, and Ireland were beginning to enjoy a bit more territory.
Gibson and half-backs Clegg and Charlie Davies were causing problems at close quarters and England should have done better when presented with a two-man overlap and the Irish line within their sights. Instead, prop Imiolek's loose pass went straight into touch.
There was no such let-off for Ireland in the 66th minute when England, having enjoyed a decent spell in the opposition's 22, moved the ball to the right and left before Burns broke the defensive line and dived in under the posts for a crucial seven-pointer.
Homer missed a penalty but starved of possession, Ireland were leaking more penalties at ruck time. Their hugely committed defensive efforts were beginning to take a toll and the London Irish starlet kicked his fifth penalty to add to Ireland's frustration.
Ruddock sprung through a rare midfield gap in the 75th minute, getting his side on the front foot. But there was no reward for the hard-working Irish as England's disciplined defence held firm, and worse followed.
Reid's attempted pass to Zebo was gobbled up by Burns who had the pace to run in the try from distance, with Homer adding the extras.
Ireland had something left in the tank, with replacement scrum-half Michael Heaney's quick deliveries demanding a final push from the forwards.
Then metres from the English line, Griffin, standing at first receiver, used a Heaney pass to step off his left and dart over for a deserved try which Reid converted.
Ireland, who finished eighth in last year's tournament, will complete the pool stages with a tough tie against Argentina on Sunday evening.
(Reprinted from RTE Sport)
