ISTANBUL - Having ended Sebastian Vettel's perfect start, Lewis Hamilton heads to the Turkish Formula 1 GP looking for ways to further close the gap to the defending World champion.When Vettel won 2011’s opening two races and took his third consecutive pole in China, talk was building that his lightning-quick Red Bull would be impossible to catch - until Hamilton beat him in China in April.With the season heading into Europe this weekend Vettel has a 21-point lead over Hamilton and is 30 ahead of the Briton's McLaren team mate Jenson Button. Vettel's team mate Mark Webber is a point behind Button in fourth.Hamilton, F1 champion in 2008, thinks the suspense is just beginning and predicts further twists in Istanbul.VETTEL STREAK ENDED"There's every reason to believe that the run of interesting and exciting races will continue," he said. "I won this race last year and Istanbul Park is a circuit I really enjoy."Vettel was undone by McLaren's strategy in Shanghai, where Hamilton took one more pit stop and had fresher tyres in the closing stages but it will take more than one glitch to upset the 23-year-old Vettel whose cool temperament is already a hallmark."We have to respect our competitors," Vettel said. "People are pushing hard, but we are pushing very hard too to maintain our strengths."Tyre strategy is likely to prove crucial again in Istanbul, especially given the cooler temperatures.Hamilton added: "We'll be seeing drivers working quite hard to look after their tyres throughout the race, particularly in Turn 8, which is fast and bumpy. It's one of the most demanding corners for tyres anywhere on the calendar."The weather could also dictate how quickly the Pirellis degrade."It's going to be a bit colder than we're used to," Button said. "The race is three weeks earlier in the season than it was last year and that might also have an effect."Webber has had to watch Vettel dominate so far in 2011, but the Australian thrilled fans with an inspired drive in China as he carved his way through the field from starting 18th to finish third.That means Vettel now has Webber to contend with again, along with the resurgent McLarens, the Ferraris of Fernando Alonso and Felipe Massa, and the aggressive Renaults of Nick Heidfeld and Vitaly Petrov."Sebastian is very fast, he's got a notable temperament and now he's also got a decent amount of experience," Webber said, “but he's not unbeatable."Alonso, meanwhile, needs a strong performance to avoid slipping out of championship contention. The double former World champion has yet to finish on the podium this season and is already 42 points adrift.Alonso's best result was fourth at the season-opener in Australia, but the Spaniard finished behind his team mate Felipe Massa when finishing sixth in Malaysia and seventh in Shanghai.DIFFICULT PERIODFerrari's lack of pace compared to the Red Bulls and McLarens has been alarming, although engineers have been working hard on improving the aerodynamics in the three weeks since Shanghai."We’re going through a difficult period. There is no point denying that our start to the season was disappointing," Ferrari's chief designer Nikolas Tombazis said. "We’ve tried to see if our approach was too conservative and we realised that, for various reasons, we were neither reactive nor aggressive enough with development."Aggression has not been lacking in Heidfeld and Petrov, each getting a third place - Heidfeld in Sepang and Petrov in Melbourne."We've shown over the first three races that we have a good car," Heidfeld said. "Istanbul could be very interesting because it is the first European race and a lot of teams will bring updates - including us."Istanbul's circuit features Turn 8 - a 640m corner that is the longest of the season its layout should give Hamilton and other challengers plenty of chances to attack Vettel."It is quite a wide track, which makes it quite safe," Petrov said. "Overtaking manoeuvres are possible so that should help make a great race." Stay with Wheels24 for the F1 weekend.