A win, should the Scot pull it off, would seal Britain's first win over the US since 1935.
Murray was rested for Great Britain's doubles match yesterday.
The British pair of Colin Fleming and Dominic Inglot, playing in place of the rested Andy Murray, were no match for Bob and Mike Bryan, who clinched a 6-2 6-3 3-6 6-1 victory in San Diego.
It left Britain leading the World Cup first-round tie 2-1 following singles victories for Murray and, brilliantly, James Ward on day one
Britain need one more win today, either from Murray's meeting with Querrey or Ward's clash with Donald Young, to move into the quarter-finals.
Following his doubles victory yesterday Mike Bryan paid tribute to Fleming and Inglot but was glad to have kept the American hosts in the tie.
He said: "I thought we played a great match against two top players.
"I think it was Inglot's first Davis Cup match and he brought it.
"They started playing great in the third set.
"I'm really happy to win this and give our team a chance."
Looking ahead to Murray's clash with Querrey, he said: "Andy is the heavy favourite, but Sam can beat anyone.
"He has one of the biggest serves in the world.
"He is going to play with less pressure than yesterday (when he lost in five sets to Ward), Andy might be a little off."
Bob Bryan added: "Andy is a grand slam champ, but Sam has beaten him before."
Andy Murray's match against Sam Querrey will get underway around 7pm GMT tonight.