London - Kevin Anderson made an impressive debut at the ATP Finals on Sunday, beating Dominic Thiem 6-3, 7-6 (12/10) as Roger Federer prepared to launch his bid for the 100th title of his storied career.
The South African giant 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 in the fourth game.
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.
"I definitely felt a little bit nervous," said Anderson. "But I was able to settle very quickly and find a really good rhythm, taking care of my serve games nicely, created quite a few opportunities on his serve.
"He wasn't serving at, you know, well, a very high first serve percentage... I think overall just getting off to a good start helped me a lot today."
Anderson, who reached a career-high ranking of number five in July, said he was getting more used to dealing with pressure situations.
"It doesn't always work out but I definitely feel like I'm getting more and more comfortable in those situations, in settings like today, against some of the best players in the world," he said.
In the later match in the Lleyton Hewitt group, second seed and six-time champion Roger Federer lost 7-6 (7/4), 6-3 to 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 replaced Rafael Nadal at the top of the rankings last week, was Sunday presented with the 2018 year-end ATP World Tour number one trophy.
He is one of only four players in ATP rankings history (since 1973) to have clinched the year-end top spot on five or more occasions, joining Pete Sampras (six), Jimmy Connors and Federer (both five times).
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)
Kei Nishikori (JPN x7) bt Roger Federer (SUI x2) 7-6 (7/4), 6-3
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) bt Nikola Mektic/Alexander Peya (CRO/AUT x7) 6-3, 6-4