UAE-based tennis fans have been treated to some thrilling action in the Dubai Duty Free Tennis Championships thus far.The high-profile tournament is now heading towards an exciting finale, with some of the highest ranked players on the planet still involved.World number one Novak Djokovic and Roger Federer both secured a berth in the quarter-finals after recording victories yesterday (February 27th).Djokovic defeated Roberto Bautista-Agut 6-1, 7-6 (7-4), while Federer overcame Marcel Granollers 6-3, 6-4.They will be joined in the last eight by Tomas Berdych and Juan Martin Del Potro, who also recorded impressive wins at the Dubai Tennis Stadium yesterday.Although Djokovic has not quite hit top gear just yet, he said he is feeling good at the moment."I think I played really, really well and a high level throughout most of the match," he remarked."And then I had another poor game like yesterday towards the end when I needed to close it out."But generally I'm feeling quite confident on the court, which is a good thing."The quarter-finals are set to take place in the city today and there are some mouth-watering matches in prospect.Serbian Djokovic will face Italian Andreas Seppi and Federer will be expecting a tough encounter against Russian Nikolay Davydenko.Meanwhile, Berdych will go up against Russian Dmitry Tursunov and Del Potro is scheduled to play German Daniel Brands.Before the competition started, the likes of Djokovic, Federer and Serena Williams hailed the wonderful organisation of the Dubai Duty Free Tennis Championships and they said that the world's top players are more than happy to compete in such a fantastic city.Major events such as this obviously attract a lot of attention and it is hardly surprising that prominent international companies are falling over themselves to sponsor sporting occasions in the Gulf.The next big event to mark in your diary is the prestigious Dubai World Cup on March 30th, which is said to be the most lucrative horseracing meeting on earth.