The Scarlets centre replaced the injured Jamie Roberts at half-time and looked set to be the villain after failing to deliver a try-scoring pass late in the second half with a two-man overlap.

But that error was banished from his memory in spectacular style when the replacement created and scored the decisive try to turn the game on its head and make it three RBS 6 Nations wins from three for Wales.

Before Williams' intervention - stealing the ball from Courtney Lawes in midfield before kicking and chasing to cross for the decisive score - 12 points from the boot of Owen Farrell looked like it was going to be enough for the home side.

But that late score, and 14 points from Leigh Halfpenny, ultimately saw Wales seal the Triple Crown on English soil for the first time in history.

Wales roared out of the blocks and might have bagged the first try of the game inside the first two minutes. Quick ball from a lineout near halfway allowed Mike Phillips to expertly put George North into space but with seemingly just Ben Foden to beat but the giant wing was felled by a David Strettle tap tackle.

Wales recycled the ball and again looked dangerous but Rhys Priestland's chip over the top went dead and England escaped the early onslaught.

Despite the early excitement the clash became confrontational yet cagey for the next 15 minutes with Wales dominating possession and territory but unable to pierce the England defence.

The deadlock should have been broken when England were penalised at scrum time after 18 minutes but Halfpenny - hero of the Scotland win last time out - sliced wide.

And that miss allowed England to draw first blood six minutes later. Wales were caught offside and Farrell - having missed with a speculative drop goal attempt when he knew the penalty was on the way - made it 3-0.

England's lead lasted just one restart however with a Halfpenny penalty making it 3-3 - after Mouritz Botha was penalised for going off his feet.

The home team responded quickly though and but for a last-gasp tackle from Wales skipper and man of the match Sam Warburton would have bagged the first try of the game through Manu Tuilagi.

That chance for the hosts went begging but they weren't denied their lead minutes later when Roberts was penalised for being offside and Farrell slotted the penalty from under the posts.

With the momentum in the England camp Farrell was a misguided second chip and chase in as many seconds away from a potential try in the corner for the home side.

And the England No. 10 was ruing his decision-making on 35 minutes when Halfpenny drew things level at 6-6 with a penalty after England wing Strettle was penalised for holding on in the tackle.

Farrell made up for his earlier transgression by sending the hosts in 9-6 to the good at the break with his third penalty from three attempts with a minute remaining.

The first real action of the second half saw England wrestle the initiative firmly in their favour when Botha charged down Priestland's kick.

England quickly recycled it and with the try-line seemingly beckoning Priestland was penalised for a deliberate offside and yellow carded allowing Farrell slotted the penalty to make it 12-6.

With Wales notorious for their inefficiency to deal with a man disadvantage England sensed blood but it was the Principality who claimed the next points on 54 minutes.

Full-back Halfpenny made it three from four - just - with a penalty after Dylan Hartley was penalised for going off his feet.

Wales despite missing the influence of centre Roberts, withdrawn with injury at half-time, welcomed back Priestland with the ten minute mini-scoreline sitting at 3-3.

Farrell, seemingly struggling with a knock, showed he was human just after the hour mark with a missed penalty - his first and only transgression - and left the fray soon afterwards.

Wales should have taken the lead with a try after 68 minutes but Roberts' replacement Williams inexplicably didn't use an overlap outside him with the try-scoring pass, and a two-man overlap, beckoning.

They were level however three minutes later when Matt Stevens was penalised for having his hands in the ruck and Halfpenny slotted an easy penalty.

But after his bad mistake earlier Williams made himself a hero with four minutes remaining with the decisive score, robbing Lawes and profitting from the friendliest of bounces after his kick ahead to gleefully touch down under the posts.

England went back down the field and Wales were forced to face a pair of lineout's on the own line and after the ball was spun out wide Strettle claimed a score in the corner.

But the Saracens wing was deemed to have been held up and with the time up Wales, and Williams, celebrated.