ROME: French Open champion Ana Ivanovic produced a maddeningly inconsistent display as she was stunned by Poland's Agnieszka Radwanska 6-1, 3-6, 6-4 at the WTA Rome claycourt International on Wednesday.

World number one Dinara Safina almost joined Ivanovic on the scrap-heap but she fought back from a double break down in the third set to beat Chinese 14th seed Zheng Jie 5-7, 6-1, 7-6 (7/3).

Fifth seed Ivanovic had a disastrous start but she regrouped and seemed to be cruising into the quarter-finals at 4-0 up in the third set after a run of winning 10 out of 13 games.

But just as her first set play had been terribly inconsistent, so her demons returned and 10th seed Radwanska reeled off the final six games to clinch the match.

It was another remarkable turn-around for the Pole who had trailed 5-2 in a third set tie-break against France's Aravane Rezai late on Tuesday night before scraping into the third round.

Ivanovic, who has struggled with injury and form since her success at Roland Garros last June, has not won a tournament this year and reached only one final.

And this performance was typical of her erratic recent form, poor to begin with, then back in the swing of things before losing her touch again at the end.

However she said she was happy with her current form on clay as she looks to defend her title in Paris later this month.

"I think I was playing pretty well, especially in the third set and the second set," said Ivanovic.

"But she played really well. After I was 4-0 up she didn't give me many opportunities.

"I feel really good. I mean, yesterday I played an unbelievable match (in beating Francesca Schiavone in straight sets) and that gave me a lot of confidence.

"And my serve is getting much better. I feel power on it. It's back. I just have to stick with the things I've been doing."

Radwanska will face fourth seed Venus Williams in the last eight after she laboured to a 6-0, 6-7 (8/10), 6-4 win over unseeded Russian Anna Chakvetadze in 2hr 20min.

The first set last only 23 minutes and world number five Venus looked like she would stroll through but Chakvetadze is a former world number five herself and she gritted her teeth and fought back to take the five-time Wimbledon champion to the brink.

Safina, meanwhile, struggled to victory in two-and-a-half hours but came close to losing a see-saw match.

She was broken four times in the first set before romping away with the second.

But she was broken again in the opening game of the decider and when she was broken again for the seventh time in the match to go down 5-2, it looked as if an upset was on the cards.

But the top seeded Russian, the sister of Marat Safin, knuckled down and ground her way back into the match to force a tie-break.

However, there was controversy in that. With Safina trailing 2-0 she contested a line call successfully when television replays suggested the original decision was right.

Instead of going down 3-0 it was 2-1 and Safina went on to win the breaker 7-3.

Even so, she was close to tears after her match.

"I'm practicing and I'm playing great and aggressive and suddenly I come on court and it's completely like 360 degrees, a completely different person playing on the court," she moaned.

"I just don't understand what's going on with me, like what is it with my brain.

"I mean, every time I go on the court I go, okay, I'm trying to play aggressive and I do totally the opposite thing.

"Way too passive and not the way that I have to play. This is just too frustrating and too sad."

Reigning two-time champion Jelena Jankovic barely had to break sweat as she coasted into the quarter-finals when Kateryna Bondarenko retired with an illness with the Serbian leading 6-1, 1-0.

World number four Jankovic will play seventh seed Svetlana Kuznetsova next after the Russian defeated home hope and 12th seed Flavia Pennetta 6-3, 3-6, 6-0.