The Irish consigned Wales to an unprecedented fifth straight home loss by beating the beleaguered reigning champions 30-22 in Cardiff, with centre Brian O'Driscoll scoring one of their three tries in a vintage performance.
England produced a similar display of intensity and energy by running through Scotland 38-18 at Twickenham to retain the Calcutta Cup, helped by a try on debut by centre Billy Twelvetrees and an 18-point haul from flyhalf Owen Farrell.
France, which is likely to be the other side challenging for the title, opens up against Italy in Rome on Sunday and will have been spurred by the early markers put down by Ireland and England.
While England's result was expected after its remarkable victory over world champion New Zealand in the autumn, the Wales-Ireland match was much harder to call.
As it turned out, the Irish were far superior, dovetailing flair with a ferocious work rate to leave Wales on an eight-game losing run heading to Paris next weekend.
Winger Simon Zebo scored Ireland's first try at Millennium Stadium after collecting a wonderful offload by O'Driscoll and then produced skills of a football player in the lead-up to Cian Healy's 25th-minute try.
Zebo flicked a misdirected pass from Jamie Heaslip up into his hands using the heel of his left foot, in a move rarely seen on a rugby pitch. The ball was recycled and Healy crashed over, making the score 17-0 and leaving Wales up against it.
Behind 23-3 at halftime, Wales conceded a close-range try to O'Driscoll — his 46th in 121 Irish tests and record 26th in the Six Nations — to virtually end the match as a contest.
"I thought he was the difference between the two teams," Wales assistant coach Shaun Edwards said of O'Driscoll, who could be appearing in his final Six Nations. "I wish someone had left him in Ireland."
A late rally resulted in Alex Cuthbert, Leigh Halfpenny and Craig Mitchell piercing the Irish defensive line but the loss continued Wales' worst run of results in a decade and left its title defence in tatters.
"It is frustrating and disappointing," said interim Wales coach Rob Howley, who is filling in for Warren Gatland while the New Zealander carries out his duties as British and Irish Lions coach. "The key in any international game is territory and possession and we came second by a very long way."
Farrell showed why many are saying he is the natural heir to Jonny Wilkinson by underpinning England's convincing win over Scotland with another composed kicking display.
The flyhalf, who is the son of England defence coach Andy Farrell, kicked seven of eight attempts at goal to squeeze the life out of the Scots and keep the scoreboard ticking over at Twickenham. He also produced a marvelous miss-pass to send over Geoff Parling for one of four England tries.
"He was cool and calm under pressure and I thought he attacked the line very well," England attack coach Mike Catt said.
Chris Ashton, Twelvetrees and Danny Care were the other try-scorers, with Twelvetrees particularly impressive with the ball in hand on his international debut as a stand-in for the injured Manu Tuilagi.
Scotland's tries came through New Zealand-born winger Sean Maitland, on his debut, and Stuart Hogg in either half but Ireland will be a much tougher rival for England at Lansdowne Road next week.
"Ireland are an outstanding side," England coach Stuart Lancaster said. "They have quality players across the board so it is a big step up. We need to make sure we are ready physically and mentally and technically."
There were 11 tries in all over the two matches, an early indication that teams are adopting an attacking approach this year.