Top seed Djokovic is attempting to match Roger Federer's record of six titles at the elite season-ending event for the top eight players of the year.
In the day's other group match, Andrey Rublev topped 2018 champion Stefanos Tsitsipas 6-4 6-4.
After his match, Djokovic was presented with the trophy for finishing the year ranked No. 1, a feat he accomplished for a record seventh time - breaking a tie with childhood idol Pete Sampras.
In an on-court interview, Djokovic recounted how he fell in love with tennis watching Sampras when he was "four or five years old" and asked his dad to buy him a racquet.
"Now I'm here and I've won this (trophy) seven times, one more than (Sampras) - incredible," Djokovic told the crowd in Italian.
"The dream continues. I hope to play this great sport for a couple of years."
Later, when asked about his on-court comments, the 34-year-old Djokovic said he doesn't have a number in mind for how many more years he wants to play.
"I don't want to impose a limit to myself at all, because I still enjoy playing tennis, and I really enjoy competition and playing at the highest level," the 20-time grand slam champion said.
"Being No. 1 in the world, there is no reason for me yet to think about leaving tennis. I really am in a good place at the moment."
After a two-month break after his loss to Medvedev in the US Open final, which ended his pursuit of a calendar-year grand slam, Djokovic returned this month and won the Paris Masters.
After gaining that early break Ruud let Djokovic back into the first set with a double-fault to be 3-3.
Ruud, a first-time qualifier, broke serve in the opening game but let Djokovic back into the first set with a double-fault to be 3-3.
From that point it seemed like it was only a matter of time before Djokovic would close out the match.
Daniil Medvedev and Alexander Zverev won their group singles on Sunday as the tournament made its debut in Turin after 12 years in London.
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