Alexander Zverev is keeping his feet firmly on the ground at the US Open even though he was aware during his third-round match that Novak Djokovic had followed Carlos Alcaraz out of the US Open. Zverev and 24-time grand slam winner Djokovic could have met in the semi-finals at Flushing Meadows but the draw has now opened up a little for the German who is still chasing a first grand slam title. Zverev, 27, outlasted Tomás Martin Etcheverry 5-7, 7-5, 6-1, 6-3 in a match that finished at 2.35 am local time Saturday, the second latest end in New York, with Alcaraz and Jannik Sinner playing until 2…