Jelena Jankovic, Caroline Wozniacki and Venus Williams all progressed to the semi-finals of the Sony Ericsson Championships after Friday's concluding group stage action in Doha.

The day started with Jankovic booking her place in the last four with a 6-2 6-2 victory over Wozniacki, who also managed to progress following Victoria Azarenka's retirement through injury during the deciding set of her White Group encounter against Agnieszka Radwanska.

And in the Maroon Group, Elena Dementieva's hopes of reaching the semis were ended by the already eliminated Svetlana Kuznetsova - a result which sent Williams through thanks to her superior percentage of sets won after all three players were tied with one victory each.

Azarenka looked on the brink of topping the White Group as she led 6-4 5-2 but after Radwanska produced a stunning comeback to force a third set, the Belarus star failed to cope with an injury to her left leg and pulled out when trailing 4-1.

The sixth seed started brightly with a break in the first game of the match and although she then immediately dropped her own service game, Azarenka then regained the upper hand with a double break to go 5-2 up before serving out the set at the second time of asking.

The second set looked like following a similarly one-sided fashion when she broke the Radwanska serve in the opener and then proceeded to roar into a commanding 4-0 lead.

At 4-1 the plucky Pole, playing her first match in the competition following the withdrawals of Dinara Safina and Vera Zvonareva, clawed back one of the breaks to keep her hopes alive but Azarenka responded in the very next game to move to the brink of the semi-finals.

However Azarenka cracked under the pressure of serving for the match as Radwanska sensationally rattled off the next five games on the bounce to take the set and force a decider.

An injury to Azarenka's left leg really began to trouble her at the start of the third set and was clearly in pain as she struggled to move at any pace during rallies.

And despite battling hard to hold serve in the second game, she soon slipped 1-4 down as Radwanska took advantage with a succession of drop shots and the agony ultimately became too unbearable to continue.

Although Radwanska's victory wasn't enough to reach the semi-finals, the Pole did pick up an extra US$100,000 in prize money for her efforts.

Earlier in the day Jankovic capitalised on Wozniacki's hamstring injury, aggravated during Thursday's dramatic win over Vera Zvonareva, to race away with a crucial triumph which followed on from her walkover success over Safina.

And despite losing to Azarenka in her opening contest, Jankovic's two wins were enough to secure top spot over Wozniacki due to their head-to-head record.

The Serbian's first breakthrough came in the fifth game when storming into a 0-40 lead and although she let one break point slip, she kept her composure on the next to move 3-2 up in the opening set.

Wozniacki, playing with a heavily strapped left hamstring, battled back bravely in the following game to earn two break points of her own but she spurned both - as well as an advantage point - as Jankovic took control.

The eighth seed stepped up another gear to swiftly claim the double break before comfortably serving out for the set, taking it 6-2 in just over 30 minutes.

Jankovic picked up where she left off at the start of the second set with an early break and then won her seventh game on the trot to move into a 2-0 lead as her opponent continued to struggle with her injury.

The match then looked as good as over when Jankovic broke once again with Wozniacki hardly able to serve with any venom whatsoever and another comfortable hold put the Serbian to within two games of victory.

Wozniacki produced a spirited mini revival to take the next two games but Jankovic got her act together again to restore the double break before serving out the match.

Meanwhile Dementieva needed a victory to progress behind group winner Serena Williams at the expense of Venus but was completely overpowered by her rampant compatriot, who surged to a one-sided 6-3 6-2 triumph.

The fifth seed had beaten Venus earlier in the tournament but straight-sets defeats against Serena, who won all three of her matches, and Kuznetsova see her bow out.

Kuznetsova broke three times throughout a largely one-sided contest in which she served superbly and finished off the consolation victory with an ace.

Semi-Final Draw:

(2) Serena Williams (USA) v (4) Caroline Wozniacki (Den)

(8) Jelena Jankovic (Ser) v (7) Venus Williams (USA)