World number one Roger Federer saved three match points to beat Andy Roddick in a thrilling Masters Cup match.
Federer celebrates his victory over Roddick
Roddick took the first set 6-4 and had three chances to win it in the second-set tie-break, but Federer clung on and took the set to level.
And one break early in the third set was enough to give the Swiss star a 4-6 7-6 (10-8) 6-4 victory in Shanghai.
Croatia's Ivan Ljubicic beat David Nalbandian of Argentina 5-7 7-6 (9-7) 7-5 in the second Red Group match.
Federer, the 2003 and 2004 champion, has now won 12 of the 13 matches he has played against Roddick, including the last eight.
And his 14th straight Masters Cup win means he is virtually assured of reaching the semi-finals, having also won his opening round-robin match against defending champion Nalbandian.
I don't know if he got nervous or it just went my way in the end, but it was really close
Nalbandian, on the other hand, is on the verge of elimination after his loss to Ljubicic.
Federer said: "It's hard to control against Andy when he's serving so big like he did in the first two sets. I know I got a bit lucky.
"Early on in the tie-break when I was down 4-1 and him serving I thought, well, I'm not playing that great and he's not giving me a chance, so I guess that's it.
606 DEBATE: Can Federer win the Masters Cup?
"But I told myself maybe I can make him nervous by just staying in the match.
"That's what happened. I don't know if he got nervous or it just went my way in the end, but it was really close."
World number five Roddick was left to rue his missed chances, and rounded on a Chinese journalist who suggested his tactic of coming to the net was a liability.
"My serve-and-volley game put me one point away (from winning) and you're saying it didn't work?" asked Roddick.
Ljubicic is overcome after winning an epic match
"I suggest learning something about tennis before you comment on it."
However, Roddick said his disappointment was tempered by the improvement in his game since he started working with Jimmy Connors.
"With the progress I've made over the last four or five months, I feel I'm getting better each time I step out on the court," he said.
"It's tough right now, but at the same time I remember where I was four or five months ago as far as my career. It definitely feels like it's on the upswing.
"For the first time in a while, I'm not getting further away," he added.
Nalbandian and Ljubicic exchanged early breaks before the Argentine broke for 6-5 and served out for the first set.
The title-holder broke immediately in the second and was two points from victory when the Croat broke back before clinching the tie-break with an ace.
Ljubicic broke for 6-5 in the final set and wrapped it up with the first of three match points when Nalbandian netted.
Red Group: Roger Federer (Swi), Ivan Ljubicic (Cro), Andy Roddick (USA), David Nalbandian (Arg)
Gold Group: Rafael Nadal (Spa), Nikolay Davydenko (Rus), Tommy Robredo (Spa), James Blake (USA)
N Davydenko v J Blake
R Nadal v T Robredo