Wimbledon champion Roger Federer came from a set down and saved two match points to end Andre Agassi's hopes of a winning return to tennis at the Masters Cup.
Federer fought a titanic battle with Andre Agassi
Federer served 20 aces on the way to his first victory over the eight-time Grand Slam winner.
The Swiss won the match 6-7 (3/7) 6-3 7-6 (9/7).
Earlier, Juan Carlos Ferrero's hopes of finishing the year on top of the world rankings took a dive when he fell to a 6-3 6-1 defeat at the hands of David Nalbandian in the first match of the season-ending tournament.
Agassi was playing for the first time in two months after joining wife Steffi Graf for the birth of their daughter Jaz last month.
Federer's win means he keeps a slim chance to win the year-end world number one ranking.
But he would have to make an undefeated title run through five matches while top-rated Andy Roddick goes winless and Ferrero wins only once.
Agassi had lost only one of nine sets in his three prior meetings with Federer, although the two had
not played since last year's Miami final.
Agassi hopes of a winning end to the season were dashed
At 4-4 in the third set, Agassi
surrendered a break in the ninth game on a pair of errant backhands.
But Federer double faulted away a break while serving for the
match and Agassi held to 5-5 on the way to a deciding tie-breaker.
Agassi hit a forehand volley winner to seize a 6-5 tie-breaker
edge but netted a backhand on match point. Federer sent a forehand
long but denied Agassi again with a forehand winner to level at
When Agassi sent a backhand wide, Federer served for the match
and smashed a forehand winner past the American to win after two
hours and 25 minutes.
Ferrero now faces tricky matches against Agassi and Federer if he is to progress and overtake Andy Roddick as world number one.
Nalbandian is the lowest ranked player in the elite Masters Cup competition, but he took his record against second seed Ferrero to two wins out of two.
Nalbandian broke Ferrero at the first opportunity to go 4-2 up in the first set, and the Spaniard never recovered.
Nalbandian took six of the next seven
games to claim the set and a commanding 4-0 lead in the second.
He closed out the win in just 67 minutes.
Nalbandian reached the US Open semi-finals in September
Ferrero said: "It's one of those days. I didn't hit any winners, and I didn't serve very well. Nothing good.
"It's the first match of the year I play like this. You
never know when it's going to come."
Nalbandian said: I didn't play for a long time, so I feel fresh, and my mind is focused."
Roddick is in the other group that has its opening matches on Tuesday.
The world number one plays Spain's seventh-ranked Carlos Moya while sixth-ranked Rainer Schuettler of Germany and fourth-rated Guillermo Coria of Argentina meet in the
other Red Group opener.