The final matches of the White Group round robin are played on Friday.
Federer and Nalbandian have been drawn in the Red Group of round-robin matches along with Ivan Ljubicic and Andy Roddick, who play later on Sunday.
No sporting event has greater popularity or higher stakes than soccer's World Cup, and they manage to sort that whole clambake out in about a month with a round-robin group stage that shifts to a single-elimination knockout round.
Djokovic beat the Swiss maestro in the final of the ATP World Tour Finals in London in November as he went back to the top of the global tree, also beating Murray in their round robin group match.
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The 22-year-old Scot won 6-3 3-6 6-2 in front of 17, 000 spectators to take an early lead in Group A of the round-robin phase.
There was huge criticism of the protracted 2007 World Cup in the Caribbean where group stages were followed by a round-robin Super Eight phase before the two semi-finals, and the tournament comprised 51 matches in total.
Second seed Zvonareva cruised past Jelena Jankovic 6-3 6-0 in the opening round-robin match in the White Group.
The 14 teams are divided into two groups of seven and after a round-robin section the top four from each group will go through to the quarter-finals.
The eight teams will play on a round-robin basis with the top two from each group progressing to the semi.
The tournament format sees the eight teams split into two groups of four for a round-robin stage, before the top two teams from each group progress to knock-out semi-finals and then the final on June 28.
Four round robin groups of four competed, with the top two in each group advancing to the playoffs on Sunday, May 27th.
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