Head-to-head* 2012 Monaco: Berdych     6-7 (4-7) 6-2 6-3* 2012 Dubai: Murray     6-3 7-5* 2011 Paris: Berdych     4-6 7-6 (7-5) 6-4* 2010 French Open: Berdych 6-4 7-5 6-3* 2006 Adelaide: Berdych     7-6 (7-2) 4-6 6-1* 2005 Basel: Murray     6-4 2-6 6-4NEW YORK - Andy Murray believes he needs to "be smart” and vary his game if he is to defeat sixth seed Tomas Berdych and reach his second US Open final.Third seed Murray has managed just two wins in six meetings against the Czech.And Murray, who has reached the semi-finals for a second consecutive year, said: "He’s a huge hitter of a ball."You need to use good variation and try not to give him the same ball over and over again, because he likes that. You need to be smart against him.”The British number one was out of sorts at the start of his quarter-final match against Marin Cilic, trailing by a set and 5-1 in the second before overpowering the Croat on the compact Louis Armstrong court.Berdych unexpectedly knocked out world number one and five-time champion Roger Federer 7-6 (7-1) 6-4 3-6 6-3 in his quarter-final and Murray has said he would have to change the game-plan he would have used against the Swiss."Even if you want to dictate points and be aggressive, he can take that away from you because he’s such a powerful guy,” said Murray of the 6ft 5in right-hander."Against Roger, Roger himself has a lot of variety so it doesn’t necessarily work against him if you use loads. But I think against someone like Tomas that’s important.”Murray has an unfavourable record against his 26-year-old opponent.Berydch’s most recent triumph was a straight-sets victory on clay in Monaco, while the world number seven has beaten the 25-year-old Scot in two of their three hard court encounters.But Murray said he would be mentally ready for the semi-final and credited coach Ivan Lendl for making a "big difference” in ensuring he is in the right frame of mind for Grand Slam matches."You never know exactly what’s going to happen in the next couple of days but I would hope that going into the match on Saturday, win or lose, I’ll be in a good place mentally,” said the Scot."I’ll fight from the first point to the last. If I do that, I’ll give myself a shot. But I can’t afford to start like I did [against Cilic] that’s for sure."I think I have improved since I started working with him [Lendl]. I’m playing better tennis and understanding how best to play the big points in the important matches.”