Belgian champion Philippe Gilbert says there can be no room for error if he is to fight off a quality field and defend his coveted Liege-Bastogne-Liege crown on Sunday. Gilbert, who grew up in nearby Remouchamps, capped a stunning fortnight of spring racing in 2011 by securing victory in cycling\'s oldest one-day classic after outfoxing the Schleck brothers Andy and Frank in a three-up finish. A year on and having switched teams from Omega-Pharma to BMC, the 29-year-old is still in the hunt for his first victory of the season. And with a handful of capable challengers biting at his heels, he will start Sunday\'s epic without the psychological advantage he held in 2011. \"I can win, but I can\'t afford to make any mistakes,\" said Gilbert, who at this point last year had already won the Fleche Brabanconne, the Amstel Gold Race and Fleche Wallonne. \"Physically, I\'m not as good as I was at this time last year but I\'m still competitive. I have to make sure I nail the perfect race.\" At 257.5 km long and with a total of 11 short, steep climbs -- nine of which are concentrated in the final 100 km -- Liege-Bastogne-Liege is considered the hardest of the hilly one-day classics. Making Gilbert\'s job harder, though, will be beating tactically astute rivals who could collaborate to make sure the Belgian isn\'t at the front after the final climb, where he can use his devaststaing finish. It\'s a scenario that Frank Schleck, the runner-up last year, is particularly keen to avoid: \"It would be hard to beat Philippe in a sprint,\" the Luxemburger said Saturday. Schleck, said to be in better form than brother and RadioShack-Nissan teammate Andy, was coy about how they would run their campaign. But he believes Gilbert -- who has shown glimpses of his 2011 form by finishing third at Fleche Wallonne -- would not be the only one to watch. \"We know who our main rivals are and which guys we need to watch. But anything is possible, there are a lot of candidates (for victory),\" said Schleck. Movistar ace Alejandro Valverde, making his return to the race having served out a doping ban which ended in January, is a former two-time winner who, like Gilbert, has a strong finish. His fellow Spaniard Joaquim Rodriguez, of Katusha, came close to winning in 2006, finished runner-up in 2009 and won the Fleche Wallonne in commanding fashion on Wednesday. Enrico Gasparotto of Astana, Liquigas leader Vincenzo Nibali and Damiano Cunego will spearhead Italy\'s hopes while Australian Simon Gerrans and Swiss Michael Albasini harbour GreenEdge\'s best chance for victory. Some of the race\'s climbs, meanwhile, are more strategic than others. The Redoute is only 2 km long at a difficult average gradient of 8.8 percent but after 220 km of racing it usually thins out the frontrunners. For GreenEdge sports director Laurenzo Lapage, this \"could be where the peloton will make the first major selection. It also the spot where we will see the race favorites test their legs.\" An arguably more strategic climb is the 1.5 km long Roche aux Faucons, whose summit is at the 238 km mark. It is where Andy Schleck made his winning move in 2009 and it could stage a final selection among a dwindling group of leaders. A long descent ensues towards the burrough of Ans, where a final climb over 1.2 km leads to the finish. Despite the \"good result\" of his third place finish at Fleche in midweek, Gilbert knows he must count on his head, as well as his legs, to get to the finish in a favourable position. \"Mentally, I feel fresh but my determination is probably stronger,\" said the Belgian. \"For me, that can make all the difference.\"