Matteo Politano came off the bench to snatch a late winner for Italy, breaking the deadlock in the 94th minute against United States.  Roberto Mancini's side toiled for much of Tuesday's international friendly in Genk but finally found a way to beat impressive goalkeeper Ethan Horvath with mere seconds remaining in added time.  Politano only came on as a substitute with three minutes to play but he dashed into the box to finish sweetly at the end of a rare incisive attack from the Azzurri.  Italy have now kept three clean sheets in a row but Mancini will be concerned about how long it took his team to break down an inexperienced United States side.  Horvath denied Federico Chiesa in the third minute, the Fiorentina forward then rifling wide of the far post.  In a lively start for the Azzurri, the busy Horvath blocked a Leonardo Bonucci effort after the centre-back was picked out by a clever free-kick from debutant Stefano Sensi.  Horvath tipped over a dipping 20-yard curler from Domenico Berardi in the 39th minute and had to be alert to push away Marco Verratti's inswinging free-kick as Italy kept pushing for the opener.  Half-time substitute Vincenzo Grifo delivered a chipped cross that Verratti could not quite jump high enough to convert as the onslaught continued after the interval.  United States, for whom Christian Pulisic became their youngest captain of the modern era, finally recorded a shot in the 63rd minute when Kellyn Acosta's free-kick found Walker Zimmerman at