Nadal, the world number two and two-times finalist, faces unpredictable German Nicolas Kiefer.

The pair have met twice this year, with the Spaniard winning in straight sets on both occasions.

Murray did not drop a set in his opening two matches but in the talented but injury-prone Haas, he faces his toughest opponent yet.

The pair have played twice before, with honours even at one win apiece.

"He's really a tough player. He's solid off both sides, serves well, volleys well, moves well. He doesn't have too many weaknesses," said Murray, 21.

"But if I serve like I did in my first couple of matches and put as many returns in the court as I did, then I'm going to have chances to break serve, put a lot of pressure on him."

In his previous win over Xavier Malisse, Murray hit 136mph on his first serve and hammered down 16 aces.

"My serve is one of the best parts of my game, winning over 80% of the points when it's going in. It's something I've worked on a lot and it's helping me out in matches," he said.

"I take a lot of confidence from managing to keep my cool and serve big in the important moments."

However, Haas's compatriot and former Wimbledon champion Michael Stich said: "The weakness in Andy's game is the second serve.

"If Tommy really exploits and attacks that and is very aggressive on it then Andy could struggle.

"If both players play their best tennis, I would still pick Tommy to win. It's a 50-50 chance but I think Tommy is the player with more experience."

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