Just what would be the impact of such a life-changing event on a man already coping with one the biggest weeks of his career, his first qualification at the ATP Finals-one of the oldest ever to do so, and after winning his first Masters and reaching his first Major semi-final at Wimbledon.
"Djokovic beat Zverev in straight sets in his second round ro" pundit and former British No 1 Greg Rusedski.
Zverev has one of the most piercing serves in the circuit and has clocked speeds over 130 miles per hour even on second serves.
"As I said, I think it can be a very, very close match". I was getting frustrated with myself about that.
Having failed to convert break points in Isner's opening two service games, Djokovic made no mistake when another chance came along, belting a forehand return for a victor and a 4-2 lead.
Victory for Cilic in three sets was one of the scenarios that would see Djokovic through before he faces Cilic himself on Friday. The World No 1 came through a tough first set 6-4 before easing through the second 6-1.
The evening session, of course, features two more over-30s in Cilic and Isner, but now the criteria had shifted a little with Djokovic's one-sided scoreline.
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It was a crucial escape for the 14-time Grand Slam champion, who stepped up the pressure on Zverev to steal a hard-fought first set.
He had points for a 4-0 and 5-1 lead but allowed world number five Zverev to hit back and win the opening set on a tiebreaker, sealing it with a sublime backhand pass.
"I started to play better in the second set and he was making a lot of unforced errors, which helped me win".
In his 11th appearance at the Finals, the Serb was guaranteed to reach the last four for the eighth time after Marin Cilic beat John Isner 6-7 (2/7), 6-3, 6-4 in Wednesday's second match.
Isner, who at 33 became the season-ending tournament's oldest debutant since 1972, applied himself admirably but barely avoided being broken a couple of times in the first set, and was broken twice more in the second set. I am just happy to be through.
Zverev missed out on a semi-final berth on his debut at the season-ender previous year and will need to beat John Isner on Saturday to have a chance of sticking around for the weekend.