North's try double was the sixth time he has achieved that feat in his 68-cap Test career as Wales claimed a biggest victory over Ireland since 1983, while it also made a major statement to British and Irish Lions head coach Warren Gatland ahead of New Zealand tour selection next month.
With about 10 minutes left to play, Ireland were driving towards the Welsh line and looked set to cross over for a try that would have given them the chance to retake the lead.
We showed we backed the coaches and we got the result.
"This is a team that never gives up and we saw that with the way we fought back, it was just a shame we couldn't finish the job", added Johnston. In November, you get to play at home mostly and I guess as frustrating at it is, I still think there was some really positive things that we did (in Cardiff).
The Championship may be out of their reach but Wales proved once again they are fighters when on the ropes with this victory over Ireland.
Recent encounters between the Celtic cousins have been closely-fought affairs, and this attritional ding-dong was no different.
He scored a try against Italy, playing through the pain barrier after suffering a thigh injury, then missed the England game before experiencing an afternoon to forget as Scotland - and their wings Tommy Seymour and Tim Visser in particular - sent Wales packing.
Rhys Webb broke clear following a lineout, then linked with Scott Williams before firing out a long pass to Leigh Halfpenny, who sent North powering over for his 29th Wales touchdown.
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Wales came battering back, but the Irish defence held firm.
"The players have been outstanding since Scotland, they've been very honest in their appraisal about the way they played in the first 15-20 minutes of the second half at Murrayfield".
Ireland coach Joe Schmidt bemoaned the sin-binning of outside-half Johnny Sexton just before the break.
Wales made their numerical supremacy pay immediately into the second period, Halfpenny doing well to follow up a Webb chip and bundle the covering, obviously injured Connor Murray into touch.
That will have to wait however, as first they must upset the Welsh at home.
The returned Sexton orchestrated an Irish fightback, Wales withstanding a remarkable 26-phase of attack before Dan Biggar was harshly penalised for a high tackle, Sexton pulling back three points.
However, Ireland dug deep and engineered an unconverted try from Hannah Tyrrell that proved to be a match victor.