Two-time US Open champion Djokovic takes on American Sandgren for the second time.
Djokovic eased to a 6-3 6-1 6-2 victory over Sandgren in the first round of Wimbledon this year.
Earlier this month, Djokovic became the first player to win the career Golden Masters (all nine Masters 1000 tournaments).
Sandgren is 2-2 against top 10 opponents in his career with both wins coming at the Australian Open in January.
How to watch Novak Djokovic vs Tennys Sandgren online
Amazon Prime Video will bring customers in the UK and Ireland live and exclusive coverage of the US Open, which takes place from 27th August to 9th September 2018 at the USTA Billie Jean King National Tennis Centre in New York, including multiple streams from several courts, catch-up highlights and full-match replays.
This extensive coverage of the Championships will be available to Prime members in the UK and Ireland for no additional cost to their membership and represents the first time a major tennis tournament has been available exclusively on a streaming service.
If you do not currently have a subscription with Amazon, you can get a free 30-day trial of Amazon Prime by registering an account.
To do this, simply head to amazon.co.uk/gp/video/offers.
Amazon Prime costs £7.99 per month but is also available for a one-off annual fee of £79.
How to watch Novak Djokovic vs Tennys Sandgren on TV
The US Open is not available to watch on TV for UK viewers.
Amazon have exclusive rights to the final major of the year after outbidding Sky.
BT customers can access the Amazon Prime Video app directly through their YouView box.
The Amazon Prime Video app can also be accessed through a compatible Smart TV.
These include, but are not exclusive to, TVs from LG, Panasonic, Samsung and Sony.