Shanghai, China -- (Sports Network) - Australian Open champion Novak Djokovic and rising Argentine Juan Martin del Potro were Tuesday's round-robin winners at the $4.45 million Tennis Masters Cup.

The second-seeded Djokovic reached the semifinals here by outlasting fourth- seeded Russian Nikolay Davydenko 7-6 (7-3), 0-6, 7-5 on Day 3 on the indoor hardcourt at Qi Zhong Stadium.

Djokovic topped Davydenko in 2 hours, 18 minutes by breaking the Russian on four occasions and firing eight aces. Davydenko could manage only two breaks in defeat.

The 21-year-old Djokovic is 2-0 and leads the four-player Gold Group, while Davydenko dropped to 1-1 for the week. The Serb is 1-1 lifetime against the gritty Russian, with both meetings coming this season.

Up next for Djokovic will be sixth-seeded Frenchman Jo-Wilfried Tsonga, the Aussie Open runner-up to the Serb back in January, while Davydenko will face the seventh-seeded del Potro. Tsonga and del Potro are making their Masters Cup debuts this week.

Thursday's Davydenko-del Potro winner will join Djokovic in the semis from the Gold Group.

The 6-foot-5 del Potro edged out Tsonga 7-6 (7-4), 7-6 (7-5) on Tuesday. Del Potro is now 1-1, while Tsonga is out of semifinal contention at 0-2.

Del Potro topped Tsonga in 1 hour, 50 minutes and withstood a 17-ace barrage from the talented Frenchman. The lanky Argentine is now 2-0 all-time versus Tsonga.

Red Group action will be staged here on Wednesday, as top-seeded Swiss Roger Federer (0-1) takes on fifth-seeded American Andy Roddick (0-1) and third- seeded Brit Andy Murray (1-0) meets eighth-seeded Frenchman Gilles Simon (1-0). Simon shocked Federer here on Monday, while Murray got past Roddick on Day 2.

Murray and Simon, like Tsonga and del Potro, are Masters Cup rookies. The U.S. Open runner-up Murray has won 15 of his last 16 matches overall, including titles in St. Petersburg and Madrid.

The 13-time major champion Federer has won this event four times, including the last two years. He topped Spain's David Ferrer in last year's finale in Shanghai.

Federer is a lopsided 15-2 lifetime against his fellow former world No. 1 Roddick, but the American is 1-0 this year, with the surprising victory coming in Miami back in April. The Swiss is a perfect 3-0 in their Masters Cup encounters.

The reigning five-time U.S. Open champion Federer is the only former Masters Cup champ in this year's field.

Murray and Simon will meet for a fourth time, with the Brit holding a 2-1 career advantage. Murray is already 2-0 against the Frenchman this year.