There was nothing to play for in terms of the tournament, with Nadal already eliminated after defeats by Taylor Fritz and Felix Auger-Aliassime, and Ruud guaranteed to win the group to progress to the semi-finals.
But, aside from extra ranking points and prize money, Nadal's 7-5 7-5 victory also gives him something to hang onto as he turns his thoughts to preparing for next season.
The 36-year-old told Amazon Prime Video: "I have been practising well just probably not enough matches to be at the level I needed to be, not enough confidence after six tough months.
"But that's how it is. Accept that things didn't go the way that I wanted. At least I finished with a positive victory. It's important. I'm happy for that."
Wins have been hard to come by for Nadal since the French Open but 2022 has still been one of the most remarkable seasons of the Spaniard's career.
Having arrived in Australia in January wondering whether a chronic foot condition might spell the end, he went on to win the Australian Open and French Open in the same year for the first time and his tally of 22 grand slam titles is more than any man in history.
"I can't ask for more - 2022, even if it has been a tough last six months, two grand slams, finishing the year in my highest point on the ranking, I can't complain at all," said Nadal.
"At my age, being able to achieve and be competitive means a lot to me. For 2023, let's try to have the proper preparation, work the right way and then start the season with the right energy and the right attitude that I need to be competitive from the beginning. I'm excited about it."
In the other late singles match, American Fritz beat Canadian Auger-Aliassime in three sets, 7-6 (4) 6-7 (5) 6-2, to progress from the Green Group along with Ruud.
Britain's Lloyd Glasspool and Finn Harri Heliovaara are through to the doubles semi-finals on their debut in Turin.
Glasspool, 28, and Heliovaara produced an excellent performance to defeat Spain's Marcel Granollers and Horacio Zeballos of Argentina 6-0 6-4 in their final round-robin match.
It was their second victory of the week after also beating Marcelo Arevalo and Jean-Julien Rojer, with their only defeat coming against Britain's Joe Salisbury and American Rajeev Ram.
Glasspool said: "It just shows how much hard work we put in and it's really nice to have it pay off. It's amazing to be able to play our best stuff on the biggest stage. We're ready for whoever comes."
Ram and Salisbury also progressed through to the semi-finals after coming from behind to beat Arevalo and Rojer 3-6 7-6 (4) 10-5 on Thursday evening for a third straight win in the Red Group.
"It was pretty tense. It is not often that you are in those kind of situations where you just need to win a set to advance," Ram said. "I think we did a really good job handling it and got better as the match went on."