Nadal struggled to convert break points but raced through the final set

Rafael Nadal moved a step closer to his first title of the year with a three-set win over James Blake to reach the Sony Ericsson Open semi-finals.

The world number two only converted four out of 19 break-points but finally ran out a 3-6 6-3 6-1 winner.

In the last four the Spaniard will play Tomas Berdych, who defeated Igor Andreev in straight sets 6-4 6-4.

Jelena Jankovic reached the women's semi-finals after world number 11 Elena Dementieva retired with a back injury.

Jankovic, 23, was leading 6-1 3-1 when Dementieva, who had the injury treated on court earlier in the match, decided she could not carry on.

They say the heat can affect your mind, too. Maybe it got to my head James Blake

Jankovic will now play Russian Vera Zvonareva, who beat her compatriot Dinara Safina 7-5 6-4.

Dementieva struggled from the outset and racked up 26 unforced errors before calling time on the match, but Jankovic also struggled physically in Florida.

"I'm fighting. I'm sick. I cannot play, I cannot breathe on the court," said Jankovic.

"I don't want to go on to the court. But I'm hanging in there and trying to be strong."

Despite her health problems she was happy with how she played in the truncated encounter.

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"I think I played pretty good tennis, especially in the first set," Jankovic said. "I was really dictating the points.

"It was my game overall that was out there on the court, and I was really happy with that.

"Unfortunately she stopped the match in the middle of the second set, and there's nothing I could do."

Nadal said: "Right now I am feeling like I am playing at my best level, so that's important, to come to the clay season with more confidence.

"He started out playing so aggressive. I didn't have many chances in the beginning. I couldn't touch the ball. I couldn't get rhythm in the beginning - nothing."

Blake looked to be struggling in the intense heat but insisted the defeat was not down to physical problems.

"I played my game for a while, and then I got a little indecisive," said Blake. "I wasn't attacking as much.

"They say the heat can affect your mind, too. Maybe it got to my head."