A shadow of space was all that separated Jelena Jankovic and Caroline Wozniacki while standing in the hallway of Khalifa Stadium prior to taking the court for today's White Group match of the Sony Ericsson Championships.

But while they stood in within reach of each other, the events of previous matches created a physical gulf between the two.

A depleted Wozniacki, who suffered cramps in both legs that caused her to collapse during her grueling two hour, 48-minute victory over Vera Zvonareva on Thursday, had little left in the tank against Jankovic today.

The eighth-ranked Serbian broke serve five times in securing her spot in Saturday's semifinals with a 6-2, 6-2 victory in 68 minutes.

The 2008 year-end No. 1 raised her record to 2-1 in the White Group to reach the semifinals for the second straight year. Jankovic joins 2009 year-end No. 1 Serena Williams and older sister Venus Williams in the final four.

"I didn't really know what to expect from her today," Jankovic said immediately after the match. "I saw what happened to her yesterday but I just concentrated on trying to win the match and get through to the semifinals."

Despite the defeat, Wozniacki also advanced to the semifinals courtesy of Agnieszka Radwanska and yet another injury.

Victoria Azarenka, who entered today's final round-robin match with a 1-1 record, needed to win to lock down the fourth semifinal spot and was poised to do just that when she took a 6-4, 5-2 lead over Radwanska, who stepped in for injured alternate Vera Zvonareva after Zvonareva replaced the departed Dinara Safina, who exited the event with a back injury.

Four points from the semifinals, Azarenka got tight. Radwanska reeled off five straight games to seize the second set then took a lead in the third when Azarenka retired with a left leg injury while trailing 6-4, 5-7, 1-4.

Venus can thank Svetlana Kuznetsova for her place in the semifinals. The reigning Roland Garros champion cracked seven aces and did not face a break point in rolling over fellow Russian Elena Dementieva, 6-3, 6-2, to eliminate Dementieva and send Venus into the final four.

Defending champion Venus has gone the three-set distance in all three of her matches. Venus, who suffered a three-set loss to Dementieva in her first match, held a match point against Serena before bowing 7-5, 4-6, 6-7(4). She bounced back to beat Kuznetsova, 6-2, 6-7(3), 6-4, yesterday.

Wozniacki admitted afterward she was emotionally deflated and physically fatigued after back-to-back punishing encounters that beat up on her body.

"After yesterday's match I was just totally dead. I got a little strain in my abdominal muscle and that didn't help much," Wozniacki said. "It was just tough luck. I got a lot of ice massage, drinking and eating and had so many bottles of fluid (after Thursday's match). I did everything I could... Definitely, I think I deserve to be in the semifinals after two great matches and such a big fight."

The inequity of the round-robin format was clear in that Jankovic, who looked listless in her 6-2, 6-3 opening-match loss to Azarenka on Tuesday, caught a break when current World No. 1 Safina retired from their White Group meeting on Wednesday after only two games. Meanwhile, Wozniacki was stretched to two hours, 58 minutes in rallying for a 1-6, 6-4, 7-5 win over Azarenka.

The physical toll of playing more than five hours in her two matches left Wozniacki looking a little spent today and Jankovic, playing crisp crosscourt combinations she sometimes disrupted with her favored two-handed backhand down the line, took full advantage.

Azarenka had punished Jankovic's serve on the opening day of round-robin play, but Jankovic won 26 of 31 first-serve points today and saved three of four break points.

"I tried to dictate the points and attack because I know how good she is in the long rallies," said Jankovic, who raised her record to 3-0 over Wozniacki in posting her first straight-sets win over the 19-year-old Dane.

Jankovic broke serve in the fifth and seventh games before serving out the set in 31 minutes.  Racing out to a 4-0 second-set lead, she never let Wozniacki have much say in the second-set rallies.