By Iain Rogers

BERLIN (Reuters) - World number two Ana Ivanovic suffered a surprise 6-2 7-5 defeat by Elena Dementieva in the semi-finals of the German Open on Saturday.

The 20-year-old Serbian, the title holder in Berlin, made far too many unforced errors and was broken five times by the Russian seventh seed.

Dementieva will play compatriot Dinara Safina in Sunday's final. The 13th seed, who has beaten world number one Justine Henin and eight-times grand slam winner Serena Williams this week, defeated unseeded Belarusian teenager Victoria Azarenka 6-4 6-1 in the first semi-final.

A runner-up at both the French and U.S. Opens in 2004, Dementieva had won all three previous matches against Ivanovic but they had never met on clay.

She held her nerve in a tight second set, striking some impressive winners, and shrieked with joy when Ivanovic skewed a backhand wide on the first match point.

"Ana was playing very aggressively and was trying to hit on every single point," Dementieva said at a news conference.

"I feel like I was more consistent and didn't make lots of unforced errors and that was the key for today's match," she added. "She's a great player but I think I was a little bit better today."

Dementieva and Safina have both won two of their previous four meetings but Safina has been victorious both times on clay.

STIFF CHALLENGE

Ivanovic was playing her second match of the day in the Steffi Graf stadium, the number two seed having earlier won the deciding set in her quarter-final against 10th-seeded Hungarian Agnes Szavay.

The pair had to abandon their match late on Friday due to bad light with the score at one set each.

"I was pretty happy with my first set this morning and I felt actually quite good going into the semi-final but today she was better," Ivanovic told a news conference.

"I felt I created a lot of chances in that second set and maybe in the key moments I wasn't as sharp as I should have been."

Safina, the 22-year-old younger sister of former men's number one Marat Safin, faced a stiff challenge from 18-year-old Azarenka in the first set, losing her serve twice.

The Belarusian appeared to be struggling with a knee injury in the second set which severely hampered her movement and Safina cruised to victory in just under 1-1/2 hours.

"If someone had told me I would be in the final I would have shaken his hand and given him half the prize money," she said, adding that this had probably been the best week of her career.

"In Russia we say that God loves three so I hope it can be third time lucky for me in the final."

Azarenka has had her best run at a tier one event in Berlin and will break into the top 20 for the first time when the rankings are updated.

Ivanovic needed to reach the final to hold on to her world number two ranking and will now be overtaken by Russian former number one Maria Sharapova.

(Editing by Clare Fallon)