Djokovic showed no signs of slowing down as he lifted the Australian, French and US Open trophies last season - with his only blip being a five-set defeat in the Wimbledon final - before securing the year-end top spot at the ATP Finals.
He wasted little time in priming himself for a tilt at a record-extending 11th trophy at the January 14th-28th Australian Open as he dismantled world number 58 Zhang in 72 minutes at a packed RAC Arena in his first match of the 2024 season.
Zheng Qinwen rolled over Olga Danilovic 6-4, 6-2 to make it 1-1 but Djokovic returned to partner Danilovic and seal a 6-4, 1-6, 10-6 victory against Zheng and Zhang.
Taylor Fritz and Jessica Pegula combined to help defending champions the United States beat Britain 2-1 in Group C as they overcame Neal Skupski and Katie Boulter 1-6, 7-6(4), 10-7.
The Americans can book their place in the quarter-finals of the $10 million team event that features 18 countries with a win over Australia on Monday.
Boulter continued her strong start to the season after an opening win over Australia's Ajla Tomljanovic as she clawed her way back from a set and 3-0 down to quell world number five Pegula 5-7, 6-4, 6-4 and put Britain up 1-0.
Fritz dragged his team into contention as he managed a left thigh problem to beat Cameron Norrie 7-6(5), 6-4.
In the only match in Sydney, Canada earned a 2-1 win over Group B opponents Chile with Steven Diez and Leylah Fernandez beating Tomas Barrios Vera and Daniela Seguel 7-5, 4-6, 10-8.
Fernandez subdued Seguel 6-2, 6-3 in the tie's opener before Nicolas Jarry won 7-5, 6-4 against Diez, who had stepped in for Canadian number one Felix Auger-Aliassime.
