By Steve Ginsburg

NEW YORK (Reuters) - Jelena Jankovic roared into her first grand slam semi-final with a stunning upset of Elena Dementieva at a water-logged U.S. Open Tuesday.

Jankovic, who considered quitting the sport after a long losing streak this year, whipped Dementieva 6-2 6-1 in 62 minutes, breaking the Russian's serve seven times in a row.

That was the only match completed before rain wiped out the rest of Tuesday's action, however, the third day of the two-week tournament that bad weather has forced matches to be postponed.

Two fourth-round matches were halted when the rain arrived. Former champion Marat Safin of Russia led German Tommy Haas 2-1 with a break of serve, and Russian Nikolay Davydenko was leading British teenager Andy Murray 6-1 5-7 6-3.

Jankovic, 21, continued her remarkable run through the tournament, earning a semi-final place on Arthur Ashe Stadium by stopping her third consecutive-top 10 opponent.

SO EXCITED

The Serbian 19th seed could hardly contain her excitement at reaching the semi-finals.

"I don't know how to explain it," she told reporters grinning broadly. "You can only know this feeling when you really are there and experience it. It's a great feeling to be in a semi-final, especially in Arthur Ashe, in a big stadium. Amazing."

Dementieva, a former Open finalist, played well but was let down by her weak serve.

"She was playing great from the beginning to the end," the 24-year-old Dementieva said. "She didn't give me any chances. I feel like she was better today. For me, it was very hard.

"I was fighting for every point, but she was just better and better. It's just unbelievable, the way she was playing today."

Jankovic lost 10 consecutive matches this year before reaching the quarter-finals at the Italian Open and she was beaten in three sets by Dementieva in the Los Angeles Open final last month.

But the Serb recalled those dark days when a first-round exit became the norm and she enrolled in college to help her ponder life after tennis.

"It was terrible, but what can I do?," she said. "I think overall in life, you're not going to always have good times. There are going to be bad times, as well.

"I think when you go through something like this, it makes you stronger as a person. For me, as a player, I feel like I appreciate my results a lot more."

Jankovic, who beat 10th-ranked Nicole Vaidisova in the third round and number seven Svetlana Kuznetsova in the fourth, will play Davenport or Henin-Hardenne in the semis.

"I think some things are meant to happen, and maybe if I didn't lose ten matches in a row, maybe I wouldn't be in the semi-finals here," she said. "I'm lucky."