2017 us open
Anderson out of Paris Masters
Going into the tournament, Anderson was in 10th position in the race to the ATP Finals with only the top eight players qualifying for the event.
It marked the fourth US Open final and third title for Nadal but the first time without Novak Djokovic on the other side of the net.
The 24-year-old was never in trouble as her defensive play derailed the 15th-seeded Keys, who was playing with a heavily bandaged right thigh.
The 4-6 6-0 6-3 6-2 thrashing also moved the Spaniard to the brink of a 16th grand slam title.
It will mark the first time two American women have played for the US trophy since 2002 when Venus and Serena Williams met.
The 31-year-old, ranked 32 in the world, is the lowest-ranked grand slam finalist since 38th-ranked Jo-Wilfried Tsonga fell at the 2008 Australian Open final.
Anderson is the first South African in 14 years to feature in the United States Open semifinals, where he will take on Pablo Carrenyo Busta.
She will meet either CoCo Vandeweghe or Madison Keys, who face each other later on Thursday, in an all American final.
Sharapova, who was granted a wildcard entry to the tournament, made too many unforced errors in a scrappy first set that featured six breaks of serve.
Roger Federer will follow Nadal on to Arthur Ashe Stadium later on Tuesday looking to hold up his end of the deal when he takes on American Frances Tiafoe.
Shania Twain saw in her 52nd birthday on Monday by performing at the US Open tennis tournament.
Roger Federer and world number one Rafa Nadal won the first three grand slam titles of the season as they came back to prominence with a bang.
The 37-year-old, who last won the title in New York in 2002, is high on confidence after reaching two grand slam finals in 2017, in Australia and at Wimbledon.
Maria Sharapova proved she will be someone to contend with for the US Open crown after the Russian wild card outlasted second seed Simona Halep.
The Scot, who had not played since Wimbledon, said he had tried everything to be fit for the final grand slam of the year, which starts on Monday.
Federer said the absence of some of the sport’s top players created an opening for lesser-known talent to emerge.
A break in each set was enough for the seventh seed to claim his third title of the year and seventh of his career.
The serenity served Thomas well after a slow start, as he bided his time before vaulting to the front with four birdies in a sizzling seven-hole stretch mid-round.
Serbia's Sportski Zurnal reported that the 30-year-old could face up to 12 weeks on the sidelines.