EDINBURGH (REUTERS) - Scotland's Jon Welsh returns to test rugby on Saturday for the first time since being at the centre of a controversial refereeing decision that cost his country a rare win at Twickenham and a place in the semi-finals of the last World Cup.

The prop is refusing to dwell on a horror call against him when he gave away a penalty for being offside in the last minute of the 2015 quarter-final against Australia, who booted over the subsequent kick to win the game by a single point.

"It is what it is. I've hardly been asked about that until recent months," said Welsh in the build-up to Scotland's opening Six Nations clash against Wales in Cardiff on Saturday, where he wins his first cap since the ill-fated incident.

"The worst thing you can do as a professional, in rugby or any sport, is to dwell on mistakes. We train hard on the rugby pitch to not make mistakes but they are going to happen.

"It's something I don't look back on at all. Obviously it's unfortunate, nobody wanted it to happen. But it did and it was on to the next thing for me."

The decision by South African referee Craig Joubert was later labelled wrong by World Rugby but Welsh took a conciliatory tone as he reflected on the heart-breaking 35-34 defeat.

Joubert adjudged Welsh to have been offside as he instinctively grabbed at the ball after it looked to have been knocked-on off the shoulder of teammate Josh Strauss.

But it was Wallaby scrumhalf Nick Phipps who made contact with the ball last before Welsh, who then should not have been deemed offside.

"He made the call. In the game of rugby you respect the ref's call. Has anybody tried to referee a game before? There are a thousand things going on. Obviously if he had gone to the TMO he would have seen it came off Phipps. It is tough for a referee. He didn't get the call right there."

Welsh went immediately off to join Newcastle in the English Premiership after the World Cup and lost his place in the Scotland side.

"I'd never abandoned hope that I'd get back into the Scotland side. I've always been in training squads or at least called back into them. I don't think the desire ever goes away to play for Scotland. I just kept training away and I've been lucky enough to be given another shot."

Saturday's match will be a 12th cap for the 31-year-old, profiting from an injury crisis among the Scotland front rowers.