BELGRADE.  Novak Djokovic failed to lead Serbia to a Davis Cup triumph on Sunday, but a streak of 24 straight victories left him upbeat for next season in which he vows to focus on Grand Slam titles.The world No 2 swept the Czech Republic’s Radek Stepanek and Tomas Berdych in straight sets, but his two points did not stop the Czechs from winning their second straight Davis Cup trophy, 3-2.Still, the wins number 23 and 24 lifted Djokovic’s spirits after a season in which he won a single major – the Australian Open – and lost the top post in ATP rankings to Rafael Nadal."It’s an incredible number considering the fact that I lost three big matches in three months – Roland Garros (semifinals) , Wimbledon (final) and the US Open (final),” said Djokovic."But I managed to bounce back and managed to play my best tennis in the last two and a half months,” he added.  "I’m full of confidence on the court and hopefully I can carry that into the next season.”The 26-year-old said he hoped the streak that brought him titles from Beijing, Shanghai, Paris and London was not over."I hope I’ll be able to retain that at the beginning of next season,” said Djokovic, who has so far clinched four Australian Open titles, and one Wimbledon and US Open title."I’ll start with the Australian Open which is the Grand Slam at which I’ve scored the most successes, and I’m looking forward to going there,” he added.After winning the Australian Open in January, Djokovic suffered a frustrating semifinal loss to Nadal at the French Open – the one Grand Slam title he has never won.That was followed by a Wimbledon final defeat against Andy Murray and another painful loss at Nadal’s hands in the US Open that eventually led to the Spaniard replacing Djokovic at the top of the world rankings.Djokovic beat Nadal in straight sets at the ATP World Tour Finals in London last Monday.