Second seed Alexander Zverev scraped through to the last 16 of the Shanghai Masters on Tuesday, winning two tiebreaks against the Netherlands’ Tallon Griekspoor in an ill-tempered match that ended 7-6 (8/6), 2-6, 7-6 (7/5). Novak Djokovic meanwhile powered through the third round, steamrolling Italian Flavio Cobolli 6-1, 6-2 in just over an hour. Zverev’s …