Second seed Amelie Mauresmo suffered a dramatic collapse as she went out of the German Open to Julia Vakulenko.
Mauresmo was playing for the first time in two months
The pair resumed their held-over last-16 match with Mauresmo leading 6-2 1-1 but the Frenchwoman won just two games on the resumption.
Ukrainian Vakulenko followed up her 2-6 6-1 6-2 win with a 6-3 5-7 6-3 victory over eighth seed Dinara Safina.
Justine Henin trailed Jelena Jankovic 3-6 4-4 in their quarter-final when play was halted by bad light.
Earlier, world number one Henin had few problems beating Maria Elena Camerin 6-1 6-3 in the last 16.
The winner of the Henin-Jankovic match will meet Svetlana Kuznetsova, who defeated Nadia Petrova 7-6 (7-5) 6-4 in Friday's first quarter-final.
I was a step slow all day. What can you do, what can you say? Just keep practising
Ana Ivanovic was the third player to reach the semi-finals as she defeated Patty Schnyder 7-5 3-6 6-4.
World number three Mauresmo was playing her first tournament after a two month lay-off to recover from an appendicitis operation.
She lost the first seven games on Friday's resumption and when she finally won a game to trail 2-1 in the final set, she shook her racquet and screamed in joy.
However, a double-fault two games later saw Mauresmo slip 4-1 down and the match was over soon after.
"What can you do, what can you say? Just keep practising," said Mauresmo. "I need the rhythm of more matches, competition. I was a step slow all day."
World number 53 Vakulenko had to go through the pain barrier in her second match of the day after hurting her foot.
"I am really pleased to have got to the semi-finals, but the game against Safina was hard, because the foot got really sore during the rain break and I had to take anti-inflammatories to dull the pain," she said.
"I am looking forward to the semi-final on Saturday, I just hope I can walk on the foot when I get up in the morning."