Murray has been struggling with a cold all week in Doha

Murray has been suffering with a cold and also looked to have a back problem as Mirnyi raced to the opening set.

An irritable Murray then slipped a break down at the start of the second but somehow found his top form to dominate the rest of the match.

Murray will next play top seed Nikolay Davydenko, who beat Olivier Rochus.

"It was a slow start for me," said Murray. "The conditions were relatively better today, still it was pretty cold out there."

Having felt under the weather all week, the last thing Murray needed was to see doubles specialist Mirnyi blitzing the net at every opportunity from the word go.

Murray plays like a rocket from the baseline - it's important for me to keep fully fit Nikolay Davydenko

The Belarusian started in great form and thoroughly deserved a 6-2 score line in the first set, as well as an early break in the second.

But with defeat looming Murray finally found his range, showing the gap in class when both men were playing well by firing a succession of passing and return winners.

The 19-year-old came through a scare in game seven of the final set, recovering from 0-40 and saving four break points to hold.

606 COMMENT: Give your thoughts on Murray's victory

And Murray then wrapped up the win with his best game of the match, breaking to love and sealing victory with a fizzing pass down the line.

Second seed Ivan Ljubicic will face Robin Soderling in the other semi on Friday.

Ljubicic came through a titanic struggle against fifth seed Mikhail Youzhny before eventually prevailing 2-6 7-6 (7-2) 7-6 (7-3).

"I'm still not happy with my serves, but today's match was not all about serves," said Ljubicic. "We played great tennis.

"I was feeling physically better, so I was able to engage him in prolonged rallies."

Sweden's Soderling was very impressive in a 6-3 6-2 win over Marcos Baghdatis.