Ireland won 31-16 to claim third place in the Autumn Nations Cup, snuffing out the visitors with a dominant second-half display at the Aviva Stadium.
The Scots, who had lost here 19-12 in the Six Nations in February, had looked the better side for the first half-hour but lost all their momentum when Duncan Taylor was shown the yellow card after 31 minutes.
The centre, who had looked impressive on his first Test start since the World Cup, was sin-binned for a deliberate knock-on.
It was a bright opening by Scotland which made the Taylor yellow card decision all the more frustrating. The inhibitions of the French game appeared to be cast aside as Townsend’s side attacked Ireland from the off.
Hogg, in particular, looked in the mood and it was heartening to see him run with ball in hand, a rare sight this autumn.
A lovely break in the seventh minute from the full-back saw him dummy and sidestep his way through a couple of Irish challenges before the ball was shipped out to the dangerous van der Merwe who was felled.
Scotland had the chance to turn their early dominance into something more tangible when Caelen Doris was penalised. Van der Walt’s penalty attempt was from all of 54 metres and the debutant struck a monster effort which rebounded off the post.
The Edinburgh stand-off got another chance a couple of minutes later when Ireland were caught offside and there was no mistake this time as he knocked over the penalty to put the Scots 3-0 ahead.
Taylor and Hogg were directing operations for the visitors, forcing Ireland on to the back foot, with Hogg causing all sorts of problems.
Much of the attack was being directed in Sexton’s direction as if Scots sensed a vulnerability in the veteran stand-off who needed patched up around his left thigh after one coming together.
Scotland doubled their advantage through another van der Walt penalty when Ireland were penalised at a scrum midway through the half, but Sexton made it 6-3 with a kick of his own after Fraser Brown had been adjudged to have made a hands-free tackle on CJ Stander.
Townsend’s side still looked the more likely and made a dangerous foray down the left as the ball was shipped quickly from Hogg to Chris Harris to van der Merwe.
Scotland kept probing and when Iain Henderson was penalised, van der Walt kicked another penalty to extend the advantage to 9-3.
The Scots had looked in control but the turning point came on 31 minutes when Taylor surged out the line to stop Bundee Aki. The Saracens centre was adjudged to have knocked on deliberately as the ball was dislodged form Aki’s grasp and Scotland suffered a double punishment, with Taylor shown yellow and Ireland awarded a penalty which Sexton duly dispatched.
Scotland, down to 14 men, were now under the cosh, defending desperately in their own 22 as momentum shifted dramatically towards Ireland.
The breakthrough came via a delicate kick to the corner from Sexton and when Robbie Henshaw outjumped Darcy Graham the ball broke free and it was Earls who was able to ground it ahead of Ali Price for the first try of the match. And although Sexton missed the conversion, Ireland had scored eight points with Taylor off the park to turn a 3-9 deficit into a 11-9 half-time lead.
Two quick tries in the first nine minutes of the second half ensured the match remained firmly in the favour of the home team.
Taylor had returned to the fray but after his ten minutes in the sin bin but the 15 men of Scotland could do nothing to stop an Irish power play finished off by Healy. A fumble by Hogg handed possession to Ireland and they made the most of it. The try came via a three-man drive and after a quick chat with the TMO, Healy’s score was awarded.
Sexton converted and there was more to come from the Irish. A slick passing move culminated in Peter O’Mahoney shipping the ball to Earls who ran in in the corner to put clear daylight between the sides. Sexton’s conversion made it 25-9 and Scotland were in desperate need of some inspiration.
Step forward van der Merwe. The big South African winger is swiftly emerging as the most potent weapon in the Scotland armoury and he bagged his third try in only his fifth Test with a thrilling run. Picking up from a ruck, he burst through two Irish challenges, pinned his ears back and streaked for the line. No-ione was going to catch him and van der Walt added the extra to reduce the deficit to nine points.
Play was briefly paused as referee Matt Carley checked out an accusation of eye-gouging, with Fraser Brown the alleged victim. Quinn Roux’s right arm appeared to make contact with the Scotland hooker’s face but the video replay failed to clarify.
Sexton made way for Ross Byrne and the replacement fly-half extended Ireland’s lead to 28-16 with a 65th-minute penalty.
O’Mahony thought he’d added to Scotland’s woes with a fourth Irish try but van der Merwe had done just enough to force the flanker’s foot into touch. There was some consolation for Ireland in the form of a penalty for an earlier no-hands tackles and Byrne clipped it over to the home side out of sight.