Roger Federer survived his toughest test in months to beat Croatian Ivan Ljubicic 6-3 2-6 7-6 (7-4) in the Masters Cup in Shanghai.
Federer failed to convert two match points in the third set and was within two points of his first defeat since losing to eventual champion Rafael Nadal in the semi-finals of the French Open on June 3.
However, the world number one controlled the decisive tie-break to extend his remarkable winning streak to 33 matches.
That moved the 24-year-old to within eight victories of Bjorn Borg's 41-match unbeaten run from 1979-80 and improved his record to 79-3 this season.
If Federer, who returned from a six-week layoff due to an injured right ankle to edge David Nalbandian on Sunday, can claim the title here, he would match John McEnroe's single-season winning percentage mark, set during an 82-3 campaign in 1984.
Federer improved to 5-0 this year against Ljubicic, perhaps his biggest threat to the title after a rash of injuries has decimated the field.
Andy Roddick, Lleyton Hewitt and Australian Open champion Marat Safin pulled out before the round-robin event, although Hewitt's withdrawal was for personal reasons rather than injury.
Ljubicic, who entered with the best indoor court record on tour this year at 34-6, controlled the second set but seemed to lose his edge early in the third.
His double fault at break point allowed Federer to take a 3-2 lead but the Croatian rallied from 5-4 down by fending off Federer's two match points and then broke to take a 6-5 lead.
Federer fought back to force the tie-break and took it 7-4 after racing into an early 3-0 lead.
In the second match on Tuesday Argentina's David Nalbandian beat compatriot Guillermo Coria 7-5 6-4.
