London - Kevin Anderson overpowered Dominic Thiem 6-3, 7-6 (12/10) to win his ATP Finals opener on Sunday as Roger Federer prepared to launch his bid for the 100th title of his storied career.
South African giant Anderson came into the match with a healthy 6-2 lead over Thiem in head-to-heads but had lost their two most recent meetings, including a straight-sets defeat at the US Open.
The Wimbledon finalist, who stands at 2.03m tall, established an early grip on the match at London's O2 arena, dominating the early exchanges and securing the crucial break.
The 32-year-old, making his debut at the season finale, won 84 percent of his points on serve in the first set, compared with just 58 percent for his ragged Austrian opponent.
Thiem tightened up his game in the second set and looked far more aggressive, with his serving numbers rocketing higher but Anderson held firm to take the set into a tie-break.
In a see-saw tie-break, 25-year-old Thiem had two chances to level the match but Anderson kept his cool to seal the victory with an ace on his fourth match point.
In the later match in the Lleyton Hewitt group, second seed and six-time champion Roger Federer takes on Japan's Kei Nishikori.
The title is contested by the eight players who have accumulated the most ranking points over the season and is in a round-robin format, with the best four players reaching the knockout semi-finals stage.
World number one Novak Djokovic, who heads the Guga Kuerten group, will be in action on Monday against John Isner while Alexander Zverev takes on Marin Cilic.
Djokovic, who is gunning for a sixth title to equal Federer's record, has stormed back to the top of men's tennis from the unlikely position of 22nd in the world as recently as June, winning Wimbledon and the US Open along the way.
Meanwhile, South Africa's doubles participant Raven Klaasen and his New Zealand partner Michael Venus lost their opening match 7-6 (7/5), 4-6, 10-5 to Britain's Jamie Murra Brazil's Bruno Soares.
Results from the first day of the ATP Finals at London's O2 arena on Sunday (x denotes seeding):
Lleyton Hewitt group
Kevin Anderson (RSA x4) bt Dominic Thiem (AUT x6) 6-3, 7-6 (12/10)
Roger Federer (SUI x2) v Kei Nishikori (JPN x7)
Jamie Murray/Bruno Soares (GBR/BRA x4) bt Raven Klaasen/Michael Venus (RSA/NZL x6) 7-6 (7/5), 4-6, 10-5
Juan Sebastian Cabal/Robert Farah (COL/COL x2) v Nikola Mektic/Alexander Peya (CRO/AUT x7)