MELBOURNE - An inspired Ana Ivanovic blew the race for the Australian Open women's title wide open when she stunned overwhelming favourite Serena Williams in the fourth round at Melbourne Park on Sunday. Novak Djokovic was for once forced to cede the spotlight to another Serbian but showed no signs of relinquishing his iron grip on the men's title and was merciless in his 6-3, 6-0, 6-2 flogging of Fabio Fognini.Third seed David Ferrer also advanced to the last eight and a meeting with Tomas Berdych and his stripy football shirt, while women's fourth seed Li Na and Flavia Pennetta set up a last eight clash of 31-year-olds. Li and Pennetta had every reason to expect their path to the final to be blocked by world number one and top seed Williams until Ivanovic secured the biggest shock of the tournament with a 4-6, 6-3, 6-3 victory on Rod Laver Arena.The Serbian's win instead sent her through to a quarter-final clash against Canadian teenager Eugenie Bouchard, who ended Australia's hopes of a home champion when she overcame Casey Dellacqua 6-7 (5-7), 6-2, 6-0. "I actually believed," said Ivanovic, whose mental toughness has been frequently questioned because of her failure to back up her 2008 French Open title. "Going on to the court today, I really just tried to give my best. I tried to make it a good match. I was very competitive till the last moment and I'm just very thrilled."Williams was riding high on a winning streak of 25 matches going back to the start of last year's U.S. Open and had not lost a single set to Ivanovic in four previous meetings. When the 32-year-old took the first set despite looking a little lethargic, she seemed to be on her way to a record 62nd victory at the Australian Open, where she is 51-1 after going 1-0 up in match.In the second set, though, Ivanovic really started to take the game to Williams, attacking the 17-times grand slam champion's serve with a success very few have managed and dictating the back court with her forehand. Her tally of 20 forehand winners to two for Williams told its own tale but, most importantly, once in front in the deciding set, Ivanovic kept her head before serving out to love for the match. "I really did certain things extremely well and I kept her under pressure I felt throughout the whole match," the 26-year-old said. "I didn't think much about the occasion and who I was playing, because it can get overwhelming."Williams's four-year quest for a sixth Melbourne title has been bedevilled by injury but she offered no excuses until realising coach Patrick Mouratoglou had let the cat out of the bag about a back problem she had suffered. "So he's the one that's snitching?" she said to laughter. "I don't want to blame anything. I feel like Ana deserves all the credit. I feel she played unbelievable today. I think she went for her shots. It's not like I gave her the match. I tried to fight the best I could today."Djokovic gave his friend of 10 years Fognini absolutely nothing in their 93-minute encounter on Rod Laver Arena and still had plenty of energy left at the end to launch into an impersonation of new coach Boris Becker. There were no jokes, however, when he was asked to assess his form after registering his 28th victory in a row and reaching the last eight for a 19th straight grand slam."I felt from the start of this tournament that I've been elevating my game as the tournament is going on. Every match is better," the second seed, who is seeking a fourth straight title, said. "The general feeling on the court, all the shots, using the court position really well, being aggressive, playing my style of the game. Mentally I was there. I was tough. I was focused. I feel great about myself in this moment. Trying to keep it up."Djokovic next faces eighth seed Stan Wawrinka, who hit 57 winners in a highly impressive display of aggressive tennis to overcome Spain's Tommy Robredo 6-3 7-6 (3) 7-6 (5) in the final match on Rod Laver Arena. Berdych reached the last eight for the fourth year in a row at the only grand slam where he has never made the semi-finals without having given up a service game let alone a set.The seventh seed's 6-2 6-2 6-3 win over Kevin Anderson was his 10th in 10 matches against the South African and left him with "plenty of gas in the tank" for his next match against David Ferrer, who beat Florian Mayer 6-7 (7-5) 7-5 6-2 6-1. Former French Open champion Li, who reached the final here last year and in 2011, allowed Ekaterina Makarova not so much as a sniff of an upset as she set up meeting with Pennetta by demolishing the Russian 6-2 6-0.Pennetta's journey to her first Australian Open quarter-final was a bit more complicated and she took 53 minutes longer to beat ninth seeded German Angelique Kerber 6-1 4-6 7-5. Li had her own particular reason for being delighted to face the Italian. "She's one day older than me, so for once I don't have to play a younger player," she beamed.