Intensity key to US dream World Cup start, says captain Ream

United States captain Tim Ream told AFP an "intense" training camp was vital to his team's dream World Cup start, as a 4-1 thrashing of Paraguay turbo-charged the co-hosts' hopes of unlikely glory.

The US squad has spent three weeks with coach Mauricio Pochettino since assembling for pre-tournament friendlies. Preparation racheted up several gears last weekend as they arrived at their California base camp.

Carrying the high expectations and intense scrutiny of being joint hosts -- along with Mexico and Canada -- the US players and staff struck a relaxed pose in front of media through the build-up.

But Ream admitted tensions had run higher behind the scenes, insisting that same passion proved essential as they ran rings around Paraguay Friday night.

"We've been together for almost three weeks, and training has been intense -- there's been some tense moments, amongst ourselves," Ream said.

"That's just a sign of guys who are ready to go, ready to get after it, and we showed that today from the very beginning" of the Paraguay win, he said.

Ream did not specify the nature of those fractious "moments", but said by the time his team took to the field in front of 70,000 fans, "I didn't have to say too much today -- we'll leave it at that."

The emphatic scoreline puts the US in a strong position to progress from Group D, with games against Australia on Friday and Turkey the following week still to come.