Wales are now just one game away from the Six Nations title and a Grand Slam after surviving a second-half fright against Scotland at Murrayfield.
Josh Adams and Jonathan Davies had the Welsh on course for a 13th consecutive win – and coach Warren Gatland’s 11th in 11 attempts against the Scots.
A depleted Scotland were roused after Darcy Graham scored on his first start and threatened to cause an upset.
But Wales held on and will clinch the title by beating Ireland in Cardiff.
It was a third defeat in a row for Gregor Townsend’s side, who travel to Twickenham next weekend searching for a first win in London against England since 1983.
Wales didn’t need to play cosmic rugby to establish their lead. Intensity and accuracy did the trick just as well against a Scottish team that was passive and error-strewn in the opening half – a side lacking in the fundamentals of aggression and concentration until they eventually found something later on and put the heat on the visitors.
It wasn’t enough to derail Wales, who survived on the back of their defence on an afternoon that brought a valuable win on a highly imperfect day. Not that Welsh fans will care about the quality. The quantity was enough. Four wins from four games. One more and it’s glory.
Scotland led through an early Finn Russell penalty but Wales dominated the rest of the first half. Wales struck their first blow and it was simple, oh so simple. The try-machine that is Adams was put away up his left wing, his finish being made a whole lot easier when Blair Kinghorn bought his shuffle and practically threw himself out of Adams’ way.
Gareth Anscombe put over the conversion and the Grand Slam-seekers were up and running. Even when Russell made it 7-6, the home respite was brief. Anscombe banged over a penalty of his own soon after, a prelude to Wales’ second try.
The try that made it 15-6 was all about Welsh grunt through the phases. Methodical, patient, accurate – Wales just took their time, inched their way forward and waited for their moment, which duly came when Davies saw some space and finished smartly.
Anscombe missed the conversion, but there wasn’t even the slightest suggestion that Scotland were going to make him regret it. The Scots had enough on their plate with their passiveness of their forwards and their startling error count, but then they started losing men through injury. Tommy Seymour exited, then Kinghorn.