Wales clinched the Triple Crown and kept their Grand Slam hopes alive with a hard-fought 16-12 win away to previous Triple Crown holders Ireland here on Saturday.
The match was all square at 6-6 when Williams gave the visitors a 51st minute lead they held for the rest of the match and on a personal note drew level with Gareth Thomas's Welsh record of 40 Test tries.
Victory made it four wins out of four for Wales under their Kiwi former Ireland coach Warren Gatland.
And their triumphant first visit to Croke Park also ended a run of eight years without a Welsh win in Dublin.
Williams said that it had been tough going but his side had deserved the win.
"We stuck at it, kept at it and deserved it at the end," he said.
"The change since the World Cup (where they went out in the first round) has had a lot to do with Warren (Gatland) and the attitude of the players.
"It has gone very well for us and we have trained very hard for it.
"The Irish played well but we had just enough in the end."
Williams, having come across to the right touchline after being fed by Stephen Jones and with not much room to work in, stepped inside Ireland wing Tommy Bowe and centre Andrew Trimble before outpacing Rob Kearney for a thrilling score and the only try of the match.
Stephen Jones converted and Wales were 13-6 ahead.
Ireland though came roaring back through a break by Jamie Heaslip and might have scored a try had not the No 8's inside pass been intercepted by Stephen Jones.
But flanker Martyn Williams became the second Wales player to be sin-binned after tripping Ireland scrum-half Eoin Reddan earlier in the move and a third successful penalty from Ronan O'Gara, who scored all of Ireland's points, cut the lead.
O'Gara then made it four from four after Wales were offside to set up a grandstand finish with Wales 13-12 ahead.
But with 10 minutes left and Wales still a point in front, Ireland suffered the dispiriting blow of seeing talismanic captain Brian O'Driscoll limp off.
Replacement Ireland forward Bernard Jackman then gave away a penalty at a ruck and James Hook, on for Stephen Jones, extended Wales's lead to 16-12.
That meant Ireland had to score a try in the final six minutes to rescue the match but Wales held out.
An attritional first-half, full of handling errors, ended with Ireland 6-3 ahead and Wales a man down after scrum-half Mike Phillips was sin-binned.
O'Gara landed both of his initial goalkicks while Stephen Jones could only manage one from three which included a miss from in front of the posts.
Ireland with hooker Rory Best and lock Paul O'Connell back in the side, looked more secure in the lineout than they had done in the 34-13 win over Scotland last time out.
But the Welsh too were largely secure on their own ball even after hooker Matthew Rees was called into the starting side following the late withdrawal Saturday of Huw Bennett with flu.
Ireland's forwards looked to draw the sting from the Welsh pack by engaging them in a series of close-quarter exchanges.
The closest either side came to a try in the opening period was in the 23rd minute when Ireland's re-shaped back three almost manufactured a score for the recalled Shane Horgan.
Kearney, making his first start at full-back after both Geordan Murphy and Girvan Dempsey were ruled out through injury, combined well with Bowe who in turn released Horgan.
The right wing cut inside a couple of attempted tackles but, in the act of trying to touch down, was well-tackled by Phillips, assisted by Shane Williams.
Referee Wayne Barnes passed the decision on to the television match official who refused to give it after replays showed Horgan had failed to get the ball on the line.
Wales should have been gone in level at half-time but saw a routine penalty chance reversed after Phillips, starting in place of Dwayne Peel, kneed Ireland prop Marcus Horan in the back and was yellow-carded.
The visitors made light of being down to 14 men at the start of the second-half with Stephen Jones making no mistake from in front of the posts after a strong drive by Wales captain and No 8 Ryan Jones.
And they were still all square when Phillips returned.
Wales will look to complete their second Grand Slam in three years at home France a week on Saturday while Ireland are away to England.