Vern Cotter does not want Scotland's positive start to the Rugby World Cup to be derailed by he considers an 'improving' United States team at Elland Road on Sunday.

The 53-year-old Kiwi -- who has turned round Scotland in terms of morale and performance -- will be looking to a radically revamped starting XV from the one that trounced Japan 45-10 on Wednesday, to beat a tough and durable US outfit.

The USA lost 25-16 to Samoa in their opening Pool B game last Sunday but they more than matched the physicality of the Pacific islanders. They scored two tries, one sparked by a superb break by impressive Ireland-born fly-half AJ MacGinty. Their discipline let them down and allowed the Samoans to keep the scoreboard ticking over.

Cotter said he expected the Americans to try to outmuscle Scotland.

"I expect them to be very physical and very direct; they have speed and size and power," said Cotter, who was plucked from French giants Clermont to take over the national side in May 2014.

"They have been improving and have worked very well to get themselves to the World Cup, they've had some good performances.

"They had a week to prepare and watched us play two days ago so they'll be on the money."

Skipper for the day Henry Pyrgos -- who steps in for Greig Laidlaw, the man of the match against Japan -- says it is imperative the Scots come out firing on all cylinders to prevent the Americans getting a toehold in the game.

"We know the USA will come really hard at us so we need to get off to a fast start," said Pyrgos.

"We have to carry the ball well, look after it and cause them problems."

Pyrgos, who has four tries to his name in his previous 16 Tests, said he felt he had the necessary qualities to counter any problems.

"I had the opportunity to captain against Ireland in the summer and I like to think I'm a pretty calm guy so nothing will change too much," said the 26-year-old England-born scrum-half.

USA coach Mike Tolkin said he thought the Scots would want to wrap up the game as early as possible because those players who had been involved in both the Japan match and the game on Sunday would begin to feel the pace.

"I don't think there is a person in the world who is not going to feel the affects of it late in the game, so they'll battle around it," said Tolkin.

"For us we want to keep taking it to them and keep the tempo and the physicality up.

"We know they want to get out to a fast start; they wouldn't want the game to drag on into the late stages and to have to slug it out for 80 minutes. I would expect a high octane pace from them."

Source: AFP