American fourth seed Serena Williams' Olympic singles debut called to a halt as she lost to Russian fifth seed Elena Dementieva in a full-set thriller in the women's singles quarterfinals of the Olympic tennis event on Thursday.

Dementieva produced an amazing turnaround to reach her second Olympic semifinal with a 3-6, 6-4, 6-3 victory over Williams.

"It's great. First of all I'm very excited on being in the semifinals of the Olympic Games. I feel like I was playing well today and I hope to continue playing like that," the 26-year-old Dementieva said in the mixed zone.

Heavy rain delayed the match for almost four hours and Williams, still in the women's doubles event with sister Venus, was keen to make up for the lost time and stormed through the opening set in only 30 minutes at 6-3.

Williams, Sydney 2000 women's doubles winner, looked on course for the semifinals when she led 4-2 in the second set. But Dementieva, who won silver in the event at the Sydney Games, took the next nine games to put herself on the verge of victory.

Williams fought back to trail 5-3 in the third set. She saved two match points in the next game but on the third, sent a forehand wide to give Dementieva victory.

"I think she started really very well. I was just trying to stay positive, trying to fight and I had nothing to lose. I was trying to play more aggressive and that was the key to the match," she added.

Russia are guaranteed a finalist in the women's singles and therefore at least one medal after Dementieva's teammate Vera Zvonareva beat Sybille Bammer from Austria 6-3, 3-6, 6-3.

"I'm very excited for the moment. I'm very excited about my semifinals here and I don't want to think about a medal. I just want to be focused on my next match and take it step by step."

Zvonareva had been expected to play only in the doubles but replaced compatriot Maria Sharapova when she withdrew from the Olympics due to a shoulder injury.

(Xinhua News Agency August 14, 2008)