Djokovic then double-faulted to give Zverev another chance to serve for the set.
The match lasted two hours and nine minutes and ended with the score 7:6 (7:5), 7:6 (7:1) in favor of Zverev.
Using a tissue to blow his nose between points, Djokovic was able to beat Zverev 6-4, 6-1 on Wednesday for his second straight victory of the tournament.
"He was up a break in both sets but it was a very important match, you don't want to start the group stages with a defeat so it's a very important win".
Djokovic entered the match having lost only one of his past 23 matches and started strongly, winning the majority of rallies from behind the baseline.
Rockets to part ways with Carmelo Anthony
Durant has a player option that many believe he will decline while Thompson will be an unrestricted free agent. As a man, as a human being you got the right to do whatever you wanna do with your life.
He is some way short of the complete article - which Lendl might remind him from time to time - but he brings energy, attitude and flair to the court, and that is gold dust for a sport that can not rely on the magic of 37-year-old Federer or 32-year-old Nadal - who is not at this tournament - for many more years.
Zverev, who has been working with Ivan Lendl in the run up to London, had the edge of Cilic in a tight match which was decided on two tie-breaks.
World number one Djokovic, though, was playing a different game, appearing little troubled by the howitzers coming off the giant Isner's racquet - breaking his opponent three times and not conceding a single break point on his own serve.
The manner of Zverev's collapse set the tone of what was to follow.
Cilic saved one match point in the 10th game as they headed into another tiebreak but Zverev powered to victory giving up only one point.
Cyclone 'Gaja' claims 11 lives in Tamil Nadu, says CM Palaniswami
The collector said reports of trees being uprooted under the impact of the cyclonic storm were received from different areas. Union Home Minister Rajnath Singh spoke to Chief Minister Palaniswami and enquired about the cyclone damage.
Earlier, Zverev kept his nerve at the key moments to beat Marin Cilic 7-6 (7/5), 7-6 (7/1), recovering from a break down in each set.
Facing each other in their opening match for a second straight year, Zverev produced the slightly steadier tennis in an attritional contest to extend his record against Cilic to 2-0 at the O2 Arena and 6-1 overall.
"To be in the semifinals here would mean a lot to me". His sole win during the group stage action a year ago, however, came over Cilic.
He faced a set point at 5-6 in the first set and survived it with a massive ace. It's going to be very tough, no doubt.
Morgan, a 35-year-old former Florida University football player, was found dead on Monday after being reported missing by his family.
Consommation : vers un ticket de caisse dématérialisé
Pour information, certaines enseignes proposent déjà à leurs clients de recevoir leurs tickets de caisse par mail. La raison environnementale enfin: chaque année un hypermarché utilise 848.000 mètres de papier en moyenne.
To find out more about him, David Law (BBC 5 Live) chats to his long-time friend and colleague Andrej Antic, a German tennis writer who has worked for Tennis MAGAZIN for over two decades. To do that point in, point out it's very hard to do against the best.