DOHA, Qatar — Venus Williams reached the semifinals of the Sony Ericsson Championships on Friday with a little help from Svetlana Kuznetsova. Jelena Jankovic also advanced by routing Caroline Wozniacki.

Kuznetsova beat Elena Dementieva 6-3, 6-2 in their last round-robin match, securing Williams' passage into the knockout round. Dementieva would have advanced with a win, but was dominated by her fellow Russian less than 24 hours after a straight-set loss to Serena Williams.

Venus Williams, Kuznetsova and Dementieva all finished with one win and two losses in their group, but the American won more sets. Serena Williams won all three of her matches.

Both Williams sisters had Friday off after playing on the first three days of the lucrative tournament, which is the last WTA Tour event of the year for the eight top-ranked women. Each round-robin win is worth $100,000, and the eventual winner takes home up to $1.55 million.

Earlier, Jankovic beat Wozniacki 6-2, 6-2 to secure her place among the last four.

The former top-ranked Serb broke twice in the first set and then raced out to a 4-0 lead in the second, facing little resistance from the 19-year-old Dane. Wozniacki can still advance from her group if Victoria Azarenka loses to alternate Agnieszka Radwanska later Friday.

"I just came out playing aggressively," Jankovic said. "I really wanted to dictate the points."

Jankovic lost to Azarenka in straight sets in her first round-robin match, and then won her second when the injured Dinara Safina retired in the third game. In total, she had spent 95 minutes on the court before a rest day on Thursday.

Wozniacki, meanwhile, won two grueling three-set matches that lasted a combined 5 hours, 48 minutes on Wednesday and Thursday, and looked like she had simply run out of energy in the hot weather.

"I didn't have anything left," Wozniacki said. "I couldn't play like I wanted to. I had some pain in my stomach muscle, as well, so I couldn't serve."

When she finally held serve for 4-1 in the second set, she raised her fist in mock triumph and laughed. She then broke Jankovic for the first time, but couldn't muster a comeback as the Serb answered with her fifth break of the match before serving it out.

Kuznetsova had nothing to play for but the cash, but had her best match of the tournament and never faced a break point. She broke twice in the second set to take a 5-1 lead, and then converted her match point with an ace.

The Russian qualified for the tournament for the fifth time, but has never advanced to the knockout round, with a combined round-robin record of 3-12.