For the first time since Wimbledon 2009, the top four players in the world made the semifinals of an event, as Victoria Azarenka, Maria Sharapova, Petra Kvitova and Agnieszka Radwanska won their quarterfinal encounters in contrasting fashion to lend the 2012 Porsche Tennis Grand Prix that unique honour.

Opening proceedings in the day session was Miami champion Agnieszka Radwanska as she took on the reigning French Open champion Li Na. Radwanska found herself a set and a break down, but battled back admirably to win the match 3-6, 6-2, 6-3. "She was playing very well today, and I think I wanted to do too much in the beginning," Radwanska said. "I was making a couple of mistakes early but in the second set I knew I had to be more calm and serve much better. It was very close and I'm happy I could turn it around and beat her on clay courts."

Top seed Rafael Nadal advanced to yet another semi-final at the Barcelona Open Banc Sabadell, comfortably beating his Serbian opponent Janko Tipsarevic in their quarter-final contest played here on Friday. While Nadal's countrymen Fernando Verdasco and David Ferrer also expectedly reached the semifinals, there was a massive upset earlier in day as Canadian youngster Milos Raonic showed glimpses of the future of tennis by disposing of world No.4 and second seed Andy Murray, as the Scotsman suffered yet another demoralizing quarterfinal defeat.

Nadal was utterly dominant as he recorded his 25th match win of the season with a 6-2, 6-2 defeat of the fifth seeded Tipsarevic. The 25-year old was broken just once throughout the match as he won 81 percent of his second serve points to advance to his seventh semi-final at the venue. Nadal will battle his Davis Cup teammate Fernando Verdasco for a place in the final. The 2010 champion faced Kei Nishikori in his quarterfinals and while this promised to be an interesting matchup, tennis fans were left disappointed as the Japanese star had to retire at 2-4 down in the opening set due to a recurrence of a back problem.

Milos Raonic caused a major upset in his quarter-final match on Friday, knocking out world no. 4 Andy Murray of Great Britain to reach the semifinals of the Barcelona Open Banc Sabadell, an ATP World Tour 500 event.

Raonic, who missed his last match up with Murray in Miami because of an ankle injury, didn't waste his opportunity this time as he notched his best career win with a 6-4, 7-6(3) victory after one hour, 45 minutes of play. Raonic was once again dominant on serve, hitting 14 aces compared to three for Murray.

He led the entire way until he was broken for the first time while serving for the match at 6-4, 5-4. The Canadian regrouped from that disappointment to dominate the second set tiebreak and come away with a straight sets triumph.

The winners of the last 4 Grand Slams all advanced to the quarterfinals of the 2012 Porsche Tennis Grand Prix, registering wins in the second round matches played today. Victoria Azarenka and Samantha Stosur overcame the challenge of their tricky local opponents Andrea Petkovic and Julia Goerges respectively, while Petra Kvitova and Li Na disposed off their opponents rather comfortably in order to also reach the quarters. Marion Bartoli and Caroline Wozniacki though suffered defeats, the former going down in a shock upset to qualifier Mona Barthel while Wozniacki was soundly beaten for the second time in a row by German Angelique Kerber.

Top seed and World No.1 Victoria Azarenka reached the quarterfinals in a way no one likes to, as her opponent Andrea Petkovic was forced to retire as she twisted her right ankle with the second set interestingly poised. The German was playing her first tour-level tournament after three months out with a back injury and this will come as a huge setback to her. Azarenka dominated the first set, taking it 6-2, but Petkovic fought back in the second set before her unfortunate injury with the scores level at 4-4. The World No.1 Belarusian, looking for her fifth title of what has been an incredible year thus far, will play another German in Mona Barthel in the quarters. The 21 year old Barthel, who had beaten Ana Ivanovic in the first round, registered her first ever win over a Top 10 player, powering down seven aces in a 6-3, 6-1 demolition of 7th seed Marion Bartoli.

The top seeds at the 2012 Barcelona Open Banc Sabadell easily advanced to the quarter-finals after resounding victories in their matches on Fridau. Leading the way were the big 2 - Rafael Nadal and Andy Murray - who dropped 5 and 3 games respectively in their third round matches today. Perhaps even more impressive was the no.3 seed David Ferrer, who dropped just 2 games to fellow Spaniard Albert Montanes. Completing the quarterfinal lineup were seeds Janko Tipsarevic, Fernando Verdasco, Feliciano Lopez and Kei Nishikori while 11th seed Milos Raonic caused a slight flutter, disposing off the No.6 seed Nicolas Almagro.

Rafael Nadal, who has not lost a match at this venue since 2003, was tested briefly, but came through comfortably enough against Colombian qualifier Robert Farah, winning 6-2, 6-3. Farah had beaten an accomplished clay courter in Spaniard Pablo Andujar in the previous round and had nothing to lose as he faced the world's best player on clay. He posed a mile threat when he rallied from a break down in the second set only to be broken twice further to lose the match. Nadal thus made it to yet another quarterfinal where he will play 5th seed Janko Tipsarevic. The flashy Serbian recorded a resounding 6-2, 6-2 win over Portugal's Federico Gil to reach the quarter-finals of this ATP 500 event.

A couple of former World No.1s, Maria Sharapova and Caroline Wozniacki won their opening matches at the 2012 Porsche Tennis Grand Prix, though not quite in the manner in which they'd have liked, their opponents, Alize Cornet and Jelena Jankovic retiring midway through their matches. Joining Sharapova in the quarterfinals was 4th seed and Miami champion Agnieszka Radwanska, the Pole registering a comfortable win over Hungarian Greta Arn.

Maria Sharapova, who was playing her first match since losing the Miami final to Radwanska (one of three finals she has lost this season), looked comfortable on the clay, as she romped through the first set 6-3. A right shoulder injury meant her opponent Alize Cornet, had to retire after the first game of the second set, but Sharapova nevertheless looked in control and will be happy with her performance. Fourth seed Radwanska was also largely untroubled as she got past Hungarian Greta Arn with a 6-3, 6-4 scoreline.