He's a big man, but Querrey gets down brilliantly to kill a backhand volley stone dead in the face of the incoming Murray. It's all looking good for the American at 40-0, but as soon as he's into a prolonged rally there is only one winner. Murray gets back to deuce but Querrey hangs on, and it's pep-talk time. Smith adopts the crouching position in front of his charge, Courier sits alongside his man like the friendly teacher who likes to be called by his first name.

The brass band is back and captain Courier has brought out the suit for a third day, which sees a smaller crowd in Petco Park as the nation prepares for something called the "Super Bowl". Murray looks keen to get back and watch it himself as he knocks off another straightforward service game.

Chantelle:, external My Davis Cup-supporting nails:

Image source, Chanwan88

Jeff Tarango
Former American tennis player on BBC Radio 5 live sports extra

"Querrey cannot deal with Murray's serve yet, and does not seem sure of his footing at all..."

Querrey plays the kind of service game he would love to have opened with, getting himself to 40-0 love with some heavy deliveries and making that backhand down the line at 40-30.

A forehand winner and an ace help Murray to 40-0 and such is his confidence that the Wimbledon champion tries to lob the 6ft 6in Querrey, who does well to scramble over an improvised volley/smash. The American then gets stuck into a couple of forehands to create space for a volley and it's 40-30, but Querrey just misses with a backhand down the line and Murray backs up the break. Captain Leon Smith is on his feet but maintaining the poker face he's had all week.

Murray opens with a return winner, which can't have settled Querrey's nerves, and the Briton already looks in a good rhythm from the baseline as he moves 0-30 up in a lengthy rally. Querrey gets on the board with a clean forehand winner but Murray responds with a brilliant cross-court forehand on the run. Two break points.... Murray nets on the first, but Querrey cracks with a forehand into the net on the second. The perfect start for Britain.

Three of the World Group quarter-finals have already been decided today, with Italy awaiting the winner in San Diego, and this year's Davis Cup will be without Rafael Nadal and Novak Djokovic in the latter stages after both were absent in defeats for Spain and Serbia.

Germany saw off the Spanish and go on to face France, while two-time defending champions the Czech Republic travel to Japan. Tomas Berdych has already warned that a hat-trick might not be on the cards as he plans to skip away ties this year. "I've won the salad bowl twice," he said. "I've given the team a lot over the past 10, 11 years. I'd say a rest would be fully deserved." In the other half of the draw, Switzerland look real contenders for a first ever title with Roger Federer and Stan Wawrinka on board, and a home quarter-final against Kazakhstan.

John Lloyd
Former British number one on BBC Red Button

"Querrey has to let it completely fly today. He's that sort of player but he'll have to take chances if he's going to be able to beat Murray today. I think he might sneak a set maybe, but I can only see on winner and that's Andy."

Ross Hutchins
British doubles player on BBC Red Button

"This is Davis Cup and it's all about 2014 Andy Murray. I very much doubt he'll let this one slip if he's fit and healthy - and he seems to be."

Image source, Reuters

"To go in 2-1 up puts us in the driving position with two matches to go, with a great chance in both of those rubbers to get a win," says GB captain Leon Smith. "Like most of the top players in the world, Andy thrives on being in this position. He's got a chance to win the tie for Great Britain, something we haven't done in the World Group for a long time.

"It's a great opportunity for Andy and our team to get through. Sam's got one of the best serves on tour, it's huge, but when James Ward started to get him moving on the court, that's maybe his weakness."

There are plenty of ways to follow the action if text-based wittering isn't to your liking. It's on the red button and 5 live sports extra right now, click the play button at the top of this page to watch BBC TV coverage of the match, and click on the live coverage tab to see options to listen to 5 live commentary. When we get to 20:20 GMT, the action will be switching from the red button to BBC Three.

Image source, Getty Images

Querrey suffered a shattering five-set defeat by James Ward on Friday, and faces a huge challenge to pick himself up against Murray. "I think the advice is pretty simple," says US captain Jim Courier. "Sam knows that he needs to play a better, more aggressive match than he did on Friday. He's going to have to take it from Andy, because one thing we know about Andy is that he doesn't beat himself. We're going to have to beat him if we want to win that match."

A victory for Andy Murray over Sam Querrey will give great Britain an unassailable 3-1 lead in the World Group first-round tie, and a quarter-final in April away to Italy. Should Querrey pull off a major upset, it will come down to James Ward and Donald Young in a fifth rubber fight to the finish.

The smart money is certainly on Murray completing the job. The Olympic and Wimbledon champion has a 5-1 record against Querrey, and showed no signs of discomfort on the clay when he beat Young on Friday. That is despite the back surgery in September that put the Scot out of action for the last two months of 2013. Fishing around for serves pounded down by the 6ft 6in Querrey will provide another marker of Murray's recovery.

Image source, Getty Images

The bases are loaded. All that's required is for Britain's biggest hitter to play up to his batting average and a first Davis Cup quarter-final in 28 years is there for the taking. Petco Park usually plays hosts to the San Diego Padres; today it could host Britain's first Davis Cup win over the USA since 1935.