ATP Finals: Kevin Anderson beats Dominic Thiem in group opener
Debutant Kevin Anderson made a confident start to his ATP Finals campaign with a straight-set win over Dominic Thiem in their group opener.
The South African world number six beat the Austrian 6-3 7-6 (12-10) at the season-ending event in London.
The match's only break came in the fourth game of the opener with Anderson then taking the second-set tie-break with an ace on his fourth match point.
Roger Federer faces Kei Nishikori later at 20:00 GMT.
The ATP Finals features the world's top eight players - minus world number two Rafael Nadal and number four Juan Martin del Potro, who are injured.
They are divided into two groups for the round-robin stage with the top two from each qualifying for Saturday's semi-finals.
Wimbledon finalist Anderson, who lost to Thiem in the fourth round of the US Open in September, took an early lead by breaking the Austrian to go 3-1 up.
Helped by his trademark big serve, which reached more than 140mph, as well as several successful dashes to the net, the 32-year-old wrapped up the first set in 41 minutes when Thiem sent a forehand into the net.
Before that Thiem had saved two set points at 5-2 when Anderson twice went long and he held on to force the South African to serve it out.
French Open runner-up Thiem cut back on his errors in the second set, putting pressure on the Anderson serve with deuces in the sixth and eighth games, but he could not make the breakthrough.
The Austrian saved three match points in the tie-break, first when Anderson netted a forehand return, then by delivering a delicate forehand and finally an ace.
But when Anderson fashioned a fourth match point with a forehand winner on Thiem's serve, the world number six smashed his 13th ace of the match to secure victory.
"It is fantastic to be here, I've worked hard and wanted to get here for so long," said Anderson, who is the first South African in 23 years to compete at the season-ending championships.
"I've watched it since I was a kid so to play here in this amazing atmosphere and get a win, I couldn't be more happy."
He celebrated the victory by getting the crowd to join in with singing Happy Birthday to his wife Kelsey, who was watching in the arena.