Wales striker Sam Vokes battles with Scotland's Gary Caldwell
Scotland are one win away from capturing the Carling Nations Cup following victory over an inexperienced Wales side in Dublin.
Wales had led 1-0 at the interval at the Aviva Stadium after a well taken goal from Robert Earnshaw.
But Craig Levein's side hit back in the second half with goals from James Morrison, Kenny Miller and Christophe Berra.
It was Scotland's first victory over Wales since February 1984.
The Scots will face hosts Republic of Ireland on Sunday while Wales play Northern Ireland in their final game on Friday.
The Welsh side included only two players - goalkeeper Boaz Myhill and defender Neal Eardley - who finished the season in the Premier League.
And on the occasion of his 53rd cap, Nottingham Forest striker Robert Earnshaw was captain for the first time.
In contrast Scotland manager Craig Levein named a near full-strength side.
Steven Naismith and Ross McCormack were the only changes from the team which lost to Brazil in March, replacing Alan Hutton and James McArthur.
In front of a sparse crowd at the Aviva Stadium it was Wales who had the first opportunity after two minutes.
But Andy King's shot from 25 yards, following Boaz Myhill's long clearance, sailed harmlessly over the crossbar.
Wales were fortunate a deflection denied an opportunity for striker McCormack following a great run and cross from Stephen Crainey.
Myhill needed to be alert to beat out a shot from Naismith after Kenny Miller led a quick counter-attack and Steven Whittaker headed wide from a Charlie Adam corner.
But Wales grew in confidence as the half progressed and captain Earnshaw and fellow forward Jermaine Easter had attempts at goal.
Wolves striker Vokes also tried his luck from 25 yards but his effort flew over the crossbar.
Bursaspor striker Miller played a one-two with Naismith but an excellent tackle by defender Darcy Blake put an end to the Scottish attack.
Levein's side continued to press and Whittaker's dangerous cross from the right eluded everyone, including Miller and McCormack.
And within a minute Blackpool midfielder Adam unleashed a 20-yard shot which deflected narrowly wide of Myhill's post.
But it was Wales who broke the deadlock and inevitably it was captain Earnshaw who scored.
The Nottingham Forest striker seized on a dreadful header by left-back Crainey following Eardley's clearance.
James Morrison celebrates after scoring Scotland's equaliser
Earnshaw kept his composure before slotting coolly past Allan McGregor to score his 15th international goal.
The goal was also significant for the fact it was the first time Wales had scored since Speed took charge of the national team last December.
Scotland's response was a McCormack effort from 10 yards which forced Myhill to stretch to his left before he safely gathered the ball.
Having left the field to a chorus of boos at the interval, Scotland started the second half the brighter of the two sides.
And they were level 10 minutes after the restart when Adam played a superb through ball for James Morrison, who fired past Myhill.
The Scots were now back in the game and Miller fired across the face of goal before McCormack's acrobatic effort from close range.
Gary Speed took the opportunity to make a number of changes, which included Celtic-bound Adam Matthews coming on to win his first cap.
Matthews and another substitute David Cotterill linked up well down the right flank but the young defender's cross failed to find Earnshaw in the middle.
But Scotland were to expose the frailties of the Welsh defence on 64 minutes and it was the captain Miller who scored their second.
West Brom's Morrison was this time the provider as he pulled the ball back for Miller to score his 14th international goal.
Six minutes later they added a third with Whittaker's pinpoint cross from the right finding Christophe Berra, who headed home at the far post.
Wales had a late chance when Earnshaw fired over but by then Scotland had done enough to secure their second victory of the competition.
Myhill, Eardley (Matthews 61), Morgan, Blake, Taylor (Gunter 46), Tudur Jones (Vaughan 72), Dorman (Cotterill 60), King (Ramsey 61), Vokes (Morison 72), Earnshaw, Easter.
Subs Not Used:
Hennessey, Collins, Gabbidon, Collison, Bellamy.
McGregor, Whittaker (Bardsley 81), Caldwell (Hanley 84), Berra, Crainey (Martin 81), Naismith, Brown, Adam (McArthur 88), Morrison (Robson 74), McCormack (Bannan 73), Miller.
Subs Not Used:
Gilks, Wilson, Forrest, Maguire, Turner.
Morrison 55, Miller 64, Berra 70.
Raymond Crangle (Northern Ireland)