With his game at a high level at the end of an unusually easy path through a Grand Slam field, Nadal overwhelmed first-time major finalist Anderson 6-3, 6-3, 6-4 on Sunday to win his third championship at Flushing Meadows.
It is the No. 1-ranked Nadal's second Grand Slam title of the year and 16th overall.
Among men, only Roger Federer has more, with 19.
Each of those two longtime rivals won two of the four majors in 2017, marking a return of both to the heights of their sport.
At No. 32, Anderson was the lowest-ranked U.S. Open men's finalist since the ATP computer rankings began in 1973.
The 31-year-old South African never had been past the quarterfinals at any major tournament in 33 previous appearances, so when he won his semifinal on Sept 8 he climbed into the stands to celebrate.
Nadal added to his U.S. Open triumphs in 2010 and 2013 and improved to 16-7 in Grand Slam finals.
For the first time since 2013, he appeared in three in a single season, losing to Federer at the Australian Open in January and beating Stan Wawrinka for his record 10th French Open trophy in June.
Nadal's career haul also includes two trophies from Wimbledon and one from the Australian Open.
Not since Pete Sampras at Wimbledon in 2000 had a man won a Slam tournament without facing any opponents ranked in the top 20.