America's Sam Querrey faces a stern test in the shape of world number two Novak Djokovic when his country meets Serbia in their first-round Davis Cup tie beginning here on Friday. Querrey, 22, made his Davis Cup bow in 2008 as a late replacement in the USA's semi-final defeat to eventual champions Spain and became one of the few players to take a set off Rafael Nadal on clay that year before going down in four sets. He can expect a similarly challenging encounter against in-form Djokovic, who recently added the ATP Dubai Open to his trophy cabinet and who has prevailed in both his previous meetings with Querrey. 'Since we played the last time Sam is a much better quality player and he has the skills and quality to be in the top 20,' said Djokovic. 'He's won against (Andy) Roddick and some other top players and this is Davis Cup so you never know what to expect, its unpredictable. 'It's going to be a tough one but hopefully with the support of the crowd we can get two wins on the first day.' Davis Cup debutant John Isner will lead 32-time champions United States into battle at the indoor claycourt Beogradska Arena when he meets Viktor Troicki in Friday's opening rubber. Djokovic's duel with Querrey follows, while America's number-one ranked doubles pairing of brothers Bob and Mike Bryan face Janko Tipsarevic and Nenad Zimonjic in Saturday's doubles. The winning team will face either Croatia or Ecuador in the quarter-finals in July. Draw: Friday (starting 1500GMT) Viktor Troicki (SRB) v John Isner (USA) Novak Djokovic (SRB) v Sam Querrey (USA) Saturday (starting 1300GMT) Janko Tipsarevic/Nenad Zimonjic (SRB) v Bob Bryan/Mike Bryan (USA) Sunday (starting 1400GMT) Novak Djokovic (SRB) v John Isner (USA) Viktor Troicki (SRB) v Sam Querrey (USA) 