Venus Williams in action in Bangalore on Friday

Bangalore: Unseeded Yan Zi of China upset world No. 4 Jelena Jankovic of Serbia 6-3, 3-6, 6-3 to storm into the semi-final of the $600,000 WTA Bangalore Open on Friday.

In a quarter final match which lasted 121 minutes, top-seeded Jankovic, who struggled with injury in the third set, failed to match the tenacity and speed of her opponent from very the early minutes. Zi used her strong double-handed returns to score the winners and led 5-3 before taking the first set.

In the second set, the Chinese, who credited the win as her biggest on the WTA tour, committed a lot of unforced errors and lost 3-6.

In the decider, Zi led 4-1. Jankovic, who had medical attention on her back and right-shoulder won two games before losing the match.

Zi had played Jankovic only once in her career and the Serbian had retired in the Bangkok open last year.

In the semi-finals on Saturday, the world No. 54 Zi will take on fourth seed Patty Schnyder of Switzerland, while the Williams sisters — Venus and Serena — squared up in the second last four match.

“I do not know but for some reasons, I had my right shoulder tight and pain on the neck today. It had not bothered me during the last three days. Pain was severe at the end of the second set. It did not bother me in my ground strokes but I was feeling the pain while serving,” Jankovic said at the post match press conference.

Praising Zi for her fine display on Friday, Jankovic said: “Yan was blocking well and was always attacking or counter attacking. I tried to get back in to the match but I was not hitting the ball well.”