The three-time world champions had come into the contest having suffered a comprehensive defeat at the hands of Brazil yesterday but took to the court at the Tauron Arena with renewed vigour as they clinched a hard-fought opening set.

The Italians were pushed even harder by the US, winner of three Olympic gold medals, in the second set but they managed to edge over the winning line to move to within one of victory.

The US, who have lost every opening game at the season-ending World League final six event since 2007, launched a brief comeback as they halved the deficit by taking the third.

Italy recovered from that setback and demonstrated why they could be a force to be reckoned with should they make the latter stages as they won the fourth set to seal a 25-22, 27-25, 26-28, 25-21 success.

Osmany Juantorena was the star of the show for the Italians as he recorded an impressive haul of 23 points as Matthew Anderson's effort of 21 for the Americans proved to be in vain.

The result saw Italy move level with Brazil in Pool K1 on one victory and they will qualify for the last four if the South Americans overcome the US tomorrow.

Poland were unable to build on their opening win as they were stunned by Serbia, much to the disappointment of the partisan crowd inside the arena.

Serbia, last year's World League runners-up, took advantage over a tired Polish side which had come through a gruelling five-set encounter with France last night as they clinched a 25-23, 25-20, 18-25, 25-18 triumph.

They will reach the semi-finals of the event if they can avenge their defeat to France in the 2015 final tomorrow.