MIAMI (AFP) - Fourth-seeded Serbian Jelena Jankovic booked a semi-final berth at the Sony Ericsson Open here on Wednesday when Russia's Elena Dementieva retired while trailing in the second-set of their quarter-final clash.

Jankovic led 6-1, 3-1 when Dementieva, battling an apparent back injury for which she received treatment after the first set, decided she couldn't continue.

Jankovic, who had saved five match points in her battling second-round victory over Sweden's Sofia Arvidsson, awaits the winner of the final quarter-final between Russians Dinara Safina and Vera Zvonareva.

Jankovic's abbreviated quarter-final echoed her experience at Indian Wells, where she reached the semi-finals when American Lindsay Davenport retired from their contest with a back injury.

The Serbian booked her fourth semi-final appearance of the year, but is still seeking to make her first final of 2008 having lost in the final four at the Australian Open, Dubai and Indian Wells.

On Tuesday, third-seeded Russian Svetlana Kuznetsova and American Serena Williams, the eighth seed and defending champion, advanced to the semi-finals.

Williams easily defeated world number one Justine Henin of Belgium, while Kuznetsova downed Venus Williams in straight sets.

Men's quarter-final action on Wednesday was headined by world number two Rafael Nadal, who took on American James Blake in a rematch of their Indian Wells quarter-final.

Nadal won that encounter in the California desert, his only victory over Blake in four career meetings.

The winner will face the winner of Wednesday's other quarter-final, between Czech Tomas Berdych and Igor Andreev of Russia.