Now to the World Group of the Davis Cup, with seventh-seeded Serbia hosting the USA in one of the key ties. The Serbs would be without 12-time grand slam champion Novak Djokovic, who is recovering from what he describes as a "small medical intervention" in an effort to cure his ailing right elbow. That would be bad news against an American squad led by the towering twosome of Sam Querrey and John Isner.

Despite going into the opening match with a big advantage in terms of experience, the 30-year-old Querrey, at the top of the screen, would be challenged in his opening set against Serbia's Laslo Djere. And the 22-year-old takes the first set in a tiebreaker to fire up the home crowd.

But the world number 12 blasts an ace to close out the second frame 6-2 and make it one set apiece.

Querrey won the third set 7-5 and now has match point as he looks to give the Americans the early lead in Serbia. And when Djere puts a bit too much mustard on that forehand, Querrey takes the fourth set 6-4, and puts the US up 1-0.

Next up is Dusan Lajovic serving to world number 18 John Isner after dropping their opening set 6-4. But the Serb takes the second in a tiebreaker 9-7.

A monster serve from Isner then gives him the third 6-3, and two sets to one lead.

However, Lajovic claims the fourth by the same score to force a fifth and deciding set.

The final frame would feature no breaks, so another tiebreaker is needed to sort out a winner. Isner attacks relentlessly, and when his forehand lands just inside the line, the 6-foot-10 American grabs the early advantage.

On match point, Isner nails a return winner to take the breaker 7-4 and give the USA a 2-0 lead.

Elsewhere, defending champions France are deadlocked with the Netherlands, while second seeds Belgium have a 2-0 lead against Hungary, and Great Britain's Cameron Norrie came from two sets down to stun Roberto Bautista Agut, and level their battle with Spain at 1-1.