England trailed the Baby Boks 11-9 at half-time at Tokyo's Prince Chichibu Stadium but turned on the power with four second-half tries curotsey Ben Youngs (Leicester Tigers), James Gaskell (Sale Sharks), Courtney Lawes (Northampton Saints) and Henry Trinder (Gloucester Rugby). London Irish full back Tom Homer converted all the tries and kicked four penalties for a personal haul of 20 points.

South Africa fought hard to contain England's huge pack and the result appeared in the balance when England held a 23-21 lead after 60 minutes. Four minutes later, the Baby Boks' challenge fell apart when flanker Rynhardt Elstadt was shown a straight red card for a dangerous tackle on Gaskell.

The match began with a string of penalties conceded by South Africa for killing the ball and Homer showed no nerves as he smashed over the kicks after two, seven and 10 minutes to build a 9-0 lead. At this early stage Elstadt and captain Rob Ebersohn were each given a cautionary word by referee Chris Pollock.

It might have set a platform for England to exploit opportunities with the ball in hand but South Africa regrouped quickly and replied with a penalty by full back Francois Brummer after 13 minutes and a try by No.8 Christiaan Stander two minutes later. Youngs had time and space to make a clearing kick just outside his 22 but Stander charged him down, hacked on and held off Youngs' attempted tackle to score at the corner.

Youngs executed a neat show and go to release Trinder on 21 minutes but the pass was ruled marginally forward. And England were rattled again when South Africa won two scrummages against the head after 26 and 32 minutes.

Homer and Brummer each fell short with long range penalty attempts before England ended the first half as South Africa had begun it, conceding a penalty for not releasing, and Brummer landed the kick from the 10 metre line to put the Baby Boks 11-9 up at the interval.

England needed a good start to the second half and they got it with a try by Youngs in the 42nd minute. Graham Kitchener leapt high in a lineout to palm the ball to his scrum half who shot through a gap, weaved 20 metres and bounced off Gerhard van den Heever and onto Brummer for a fine score. Homer converted.

A textbook clearout at a ruck earned England a turnover, reminding them of their early success and the backs were encouraged to move the ball through the hands. But when Homer was eventually tackled in the South Africa 22, and flanker Marnus Schoeman was given the Baby Boks' third warning for not releasing, England chose to kick out for a lineout and nothing came of it.

South Africa may have seen that as a narrow escape and they retook the lead after 54 minutes. Fly half Lionel Cronje grubber-kicked, Charlie Sharples and Homer made a muddle of clearing up for England and centre Nicolaas Hanekom ran through to score, with Brummer converting for 18-16. Then a third penalty by Brummer on 58 minutes nudged South Africa out to 21-16.

The nip and tuck nature of the match continued as Youngs' pass from a ruck in the 22 bounced up for Gaskell to gallop through three tackles for England's second try converted by Homer: 26-21.

The death knell sounded for South Africa after 64 minutes. Elstadt was sent off after he flipped Gaskell over in mid-air and allowed the Sale lock forward to crash to the ground, shoulder first. Referee Pollock consulted with French assistant referee Pascal Gauzere before brandishing the red card, and Homer kicked the resulting penalty.

With 70 minutes gone England had their third try when Kitchener caught a lineout and Lawes was the scorer at the base of a powerful drive, with Homer converting again for 33-21.

And this repeat of the 2008 semi final - when England defeated South Africa 26-18 in Cardiff - was settled by Trinder's try, converted by Homer, after No.8 Carl Fearns' short charge up the middle and slick passing along the line.

England had reached the last four by defeating championship hosts Japan, Scotland and Samoa in Pool B, scoring 125 points and conceding just two tries. They now have the chance of revenge over the reigning champions New Zealand, who won last year's final 38-3 in Wales and cruised past Australia 31-17 in today's first semi final at the Prince Chichibu Stadium.

South Africa U20: Francois Brummer; Gerhard van den Heever, Nicolaas Hanekom, Robert Ebersohn (capt), Sampie Mastriet; Lionel Cronje, Ross Cronje; Morne Mellet, Kyle Cooper, Coenraad Oosthuizen, Jan Andre Marais, David Bulbring, Marnus Schoeman, Rynhardt Elstadt, Christiaan Stander. Replacements: Zane Botha for Cooper 59, Caylib Oosthuizen for Mellet 65, Kenechukwu Ofakor for Marais 56, Yaasir Hartzenberg for Stander 71-77, Johan Sadie for Hanekom 74. Not used: Julian Redelinghuys, Rudy Paige.

Sent off: Elstadt 64.

Scorers: Tries: Stander, Hanekom; Con: Brummer; Pens: Brummer 3.

England U20: Tom Homer (London Irish); George Lowe (Harlequins), Henry Trinder (Gloucester Rugby), Luke Eves (Bristol Rugby), Charlie Sharples (Gloucester Rugby); Rory Clegg (Newcastle Falcons), Ben Youngs (Leicester Tigers); Ben Moon (Exeter Chiefs), James Clark (London Irish), Bob Baker (London Wasps), Graham Kitchener (Worcester Warriors), James Gaskell (Sale Sharks), Courtney Lawes (Northampton Saints), Calum Clark (Leeds Carnegie, capt), Carl Fearns (Sale Sharks). Replacements: Jamie George (Saracens) for J Clark 33, Shaun Knight (Gloucester Rugby) for Baker 56, Jack Cobden (Leicester Tigers) for Sharples 59. Not used: Dan Williams (Gloucester Rugby), Josh Ovens (Bath Rugby), Dave Lewis (Gloucester Rugby), Rob Miller (Newcastle Falcons).

Scorers: Tries: Youngs, Gaskell, Lawes, Trinder; Cons: Homer 4; Pens: Homer 4.

Referee: Chris Pollock (New Zealand)

ends