Listen to Sportsound commentary from Murrayfield
Richardson goes over early before Van der Merwe scores in 50th cap
Graham & Dobie add further scores in opening 20 minutes
Van der Merwe, Dobie & Graham get second tries as Scots run riot
Graham & Dobie complete hat tricks; Rowe, McDowall, Horne & Smith also cross
Scotland play opening Autumn Nations Series game
Townsend's team also face New Zealand, Argentina and Tonga this month
Scotland 50-0 USA
Rory Lawson
Former Scotland captain on TNT Sports
The person purring most will be Lee Radford, the Scotland defence coach.
It's 50 points to zero, a big donut, and he'll be desperate it to keep it that way.
Zero clean breaks for the US Eagles so far this afternoon, as well.
Scotland 50-0 USA
Max Williamson is on, as is George Horne.
But it's Darcy Graham who the latter replaces, with Jamie Dobie shipped out to the wing. No further scores for the Hawick flyer.
Scotland 50-0 USA
Rory Lawson
Former Scotland captain on TNT Sports
I've got a funny feeling that Makeen Alikhan has been told to come on and ruffle some feathers...
Scotland 50-0 USA
There's a player without a shirt on. In a scuffle with Nathan McBeth, US substitute Makeen Alikhan is left topless and decides to just play on.
Moments later, he tries to rip the shirt of Stafford McDowall. Getting cold, are we?
Paddy Harrison steams in as the enforcer, and it's all a bit silly. Whatever stops Scotland scoring, I guess?
Scotland 50-0 USA
Colin Gregor
Former Glasgow Warriors back on BBC Radio Scotland
It's a well executed try from Scotland, but it's all a little too easy.
Darcy Graham
Scotland hit the 50-point mark just three minutes into the second half.
Kyle Rowe is able to free Graham down the right. He plays the one-two with Ollie Smith, and adds his third of the game.
He's level with Duhan van der Merwe in this tit-for-tat race at the top of the all-time scorers list.
Scotland 45-0 USA
Those subs then. Nathan McBeth and Murphy Walker are both on in the props, with Alex Samuel on behind them, and Magnus Bradbury behind him.
In the backs, Ross Thompson is on for Adam Hastings who is off for an HIA, sustained in the final play of the first half. We could see on the wee TVs that his mouthguard was flashing.
Scotland 45-0 USA
Not the start to the second half that the Scots wanted, as substitute Alex Samuel sees the ball bounce off his chest as he tries to gather the kick off.
Plenty of changes at the half for Scotland. We'll bring you them all shortly.
HT: Scotland 45-0 USA
Image source, SNSDarcy Graham goes over in the corner for his second...
Image source, SNSAfter Jamie Dobie has gone in under the posts.
HT: Scotland 45-0 USA
Peter Wright
Former Scotland prop on Sportsound
It's 15 guys playing for each other. No forward stucks out, but the breakdown work is really accurate, they're getting really quick ball.
The wingers have scored four between them, so it shows we're putting width on the ball.
The USA look really unfit. I know they've just qualified for the World Cup, but it's disappointing. As soon as it gets to three or four phases, guys are walking. Scotland aren't sweating at that point.
HT: Scotland 45-0 USA
Tom English
BBC Scotland chief sports writer
All Scotland can do is make a really, really poor team look really, really poor - and that's exactly what they're doing.
Sympathy for the USA because their domestic rugby scene is chaotic and self-defeating, and they are completely and utterly out of their depth here.
But Scotland have been patient and ruthless.
I predicted a 50-point win, and big Peter Wright looked at me somewhat quizzically. I should have gone for 60 instead.
There goes the half-time whistle, and it's been parma-violet perfection from Scotland.
Seven tries and a record 45 unanswered points from the Scots in the first half. They have blown a poor USA side away.
Are you watching, are you watching, are you watching Donald Trump?
Image source, SNSDuhan van der Merwe says goodnight to a US defender
Scotland 45-0 USA
John Barclay
Former Scotland captain on TNT Sports
Some USA players fly in, some not.
Complete uncertainty.
There's a lack of cohesion for them - if one goes in, they all have to go in.
Darcy Graham
A try that draws "oohs" and "aahs" from the home support. A french word sums it up nicely though - joué.
Scotland steal a line-out and fire it out wide. There's fast hands from Adam Hastings and Kyle Rowe, which puts Graham over in the corner.
It was Liam McConnell who stole the line-out, by the way.
Scotland 40-0 USA
Mind you, they almost did there!
From a US throw on the edge of Scotland's 22m, Scotland manage to hack the ball down the field and hooker Paddy Harrison is chasing after it.
A slip allows him to boot it over the try line, but a US defender is back to touch down.
Scotland 40-0 USA
Sorry about the delay.
There's not been an issue with the live feed, Scotland just haven't scored for a few minutes.
Scotland 33-0 USA
John Barclay
Former Scotland captain on TNT Sports
All the problems stem from the USA's inability to make good reads on Scotland's attack.
Jamie Dobie
Dobie at the double for Scotland.
Stafford McDowall dummies one and spots a gap, cutting through with ease. He plays in Dobie, who sprints in under the sticks - again.
All too easy for Scotland.
Scotland 33-0 USA
Andy Burke
BBC Sport Scotland at Murrayfield
A really professional performance from Scotland so far.
They have been ruthless and five tries in under 25 minutes has effectively killed the game.
Keep the foot down until half-time then we can expect some changes as Gregor Townsend starts looking ahead to next week and the All Blacks.
Duhan van der Merwe
The big winger uses his big shoulder to shrug off a last-ditch defender and score in the corner, his second of the night and Scotland's fifth.
"Boomfa!" as they say back in South Africa.
"Sit doon!" as they say back here.
