This year’s beaten Wimbledon finalist saw off the Japanese fifth seed 6-3, 7-6 (7/3) to join Rafael Nadal, Novak Djokovic, Juan Martin del Potro, Roger Federer and Alexander Zverev in London next month.
The identity of the last two ticket holders will be determined at the Paris Masters starting Monday, with Nishikori still in with a shout of making the elite eight-player cast list.
The last South African singles player to make it to the season-closing showpiece was Wayne Ferreira in 1995.
Anderson’s success in Vienna was the biggest of his career to figure in the ATP Top 10 for the first time.
“It has been a huge goal of mine all year to make it to London. I have said that right from the beginning,” the second seed said. “To finally put my name there feels fantastic.”
This was his fifth final of the year and his second title after the inaugural New York Open in February.
New York and the 32-year-old’s previous three career wins came in Johannesburg, Delray Beach and Winston-Salem were all at World Tour 250-level.
And he was thrilled to finally secure a World Tour 500 trophy.
“It means a lot. It has been a long time coming… any time you make a final, you want to put the history behind you and it was always going to be a tough match,” said Anderson.
“I was up against an unbelievable opponent in Kei and I really had to play some amazing tennis. I couldn’t be more pleased to have kept at it and finally broken through at this level.”
Nishikori, who has lost eight ATP finals since his last win in Memphis in 2016, is still in with an outside chance of joining Anderson and company in London.
He is 325 points behind eighth-placed Dominic Thiem heading to Paris.
Nishikori saved two first set points but lost it on the third when he was unable to deal with a driven backhand.
A tight second set went to a tiebreak with Anderson landing his 13th ace of the match to win his landmark title. DM
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