If Andy Murray is to win the Sony Ericsson Open in Miami this weekend then he will have to beat one of the greatest players in history and then, perhaps, the greatest player of the moment.

The Scot takes on Rafael Nadal in the semi-finals here today, trying to reach his third final of the year and improve a 5-13 record with the Spaniard.

The world No 1, Novak Djokovic, who was due to take on David Ferrer of Spain in the last eight in the early hours of this morning, is seeded to reach the final. It shows the enormity of Murray's task.

But having shaken off his early defeat in Indian Wells, Murray looks to be a man in form and the Scot may actually be the favourite to reach the final.

Not only is Nadal still not at full steam after missing the whole of February to rest, the world No 2 is also struggling with a sore knee, an injury that will affect him mentally, almost as much as physically.

"It's always a pleasure for me to play Andy," Nadal said. "He pushes you to the limit on everything. But the negative thing is I have to recover well. I have to improve my knee if I really want to have any chance to win. If not, it's going to be almost impossible."

Win or lose, Nadal will be fairly content with his efforts in both Indian Wells, where he made the semi-finals, and in Miami, where he lost in the final last year to Djokovic.

Murray needed a couple of stomach pills to settle him down in his quarter-final win over Janko Tipsarevic of Serbia.

The Scot believes he over-hydrated in the build-up to the match and at one point, he felt like burping and when he tried to drink, he "wanted to throw up".

Murray has won just five of his 18 meetings with Nadal, including semi-final defeats at the French Open, Wimbledon and the US Open in 2011.

But the Scot did win their last encounter, in the final in Tokyo in October, and will fancy his chances, particularly with Nadal perhaps a little below par.

Not that Murray will make the mistake of under-estimating a man who has won 10 grand slam titles and who never knows when he is beaten.

"I've always quite enjoyed playing Rafa on hard courts," Murray said. "He's obviously very tough for everybody and he's played well here the last couple of years.

"I think it's a good, good court for him, pretty good conditions. He's obviously playing some good tennis, semis last week and winning the doubles."

However, it is the way Murray is playing himself that could be the key to the outcome of the match.

When he was beaten by the Spanish world No.92 Guillermo Garcia in Indian Wells, Murray pledged to figure out what went wrong and to put it right.

That meant spending a week in Miami with his coach Ivan Lendl and the results are clear for everyone to see.

Standing closer to the baseline than before, Murray is dominating more of the rallies and doing less running, which saves his energy for the closer matches.

It is still a work in progress – there will be days when his new-found aggression and re-worked forehand don't pay off – but so far, so good.

"The match against Tipsarevic was really important for me to get through, having to fight back after being a break down a few times in the second set," he said.

"And then also, at the end of the third set when I was up a break, he had break point in a tight game and I came up with some big serves and served my way out of trouble, which is important.

"It's good to be in the semi-finals and hopefully I can rest, recover, and play well."

In the women's event, Maria Sharapova came from a set down to beat Caroline Wozniacki 4-6, 6-2, 6-4 to book her place in the final.

The Russian led 4-1 in the first set before losing five games in a row but recovered to set up a final against the winner of last night's clash between Agnieszka Radwanska and Marion Bartoli.