Miami - An irate Roger Federer smashed a racket for the first time in memory as the normally calm Swiss stumbled to a 3-6, 6- 2, 6-3 loss against Novak Djokovic in the Miami Masters semi-finals on Friday.

Federer reduced his Wilson to scrap in a flash in the third game of a frustrating final set against the third seed as the Serb claimed a 3-0 lead after winning his sixth straight game in a turnaround.

At one point, Federer lost five of six service games.

"I just tried to keep my focus," said Djokovic. "I was on a roll in this period of the match, so I just tried to continue on playing patiently and win."

A frustrated Federer will turn his attention to the clay season less than 24 hours after Argentine Juan Del Potro dispatched number 1 Rafael Nadal in the quarter-finals.

Sixth seed Del Potro will bid for the final against 2008 Australian Open winner Djokovic when he faces on-form Scot Andy Murray later in the last four.

"I struggled with my timing, it was a tough finish for me," said Federer, yet to win a title this season. "It was already gonna be tough in the wind. I struggled heavily today."

Federer said it was tough as the match drifted away: "You try hard and nothing is working. Once you start feeling bad it's tough to regroup. At one end there was sun in the eye, but it the same for both players.

"Once one guy gets the upper hand and the other is uncertain, it's tough. He struggled big time in the first. But I finished even worse than him."

Djokovic reversed a run of two straight losses to Federer with his effort in one hour, 46 minutes, striking 20 winners and breaking the second seed six times.

Federer's form suddenly fell off a cliff after he won a comfortable first set in 31 minutes. Djokovic profited despite his opponent's mini-comeback trailing 0-4 in the third.

The Swiss broke back for 1-4 and finished the eighth game with a pair of aces, but Djokovic served out victory a game later.

"I've had the biggest success against him on hard courts," said Djokovic. "But I knew also that I always started the matches quite impatiently and more aggressive than I needed to.

"That was the scenario in the first set today. Even though I served really well, I was quite nervous and making lots of unforced errors.

"But then it changed. I was just playing smarter afterwards. I just waited more, was more patient and created the opportunity to make a winner while waiting for his unforced errors.

"We kind of changed the roles, 3-2 in the second set (Djokovic broke on his fifth chance of the game) was a key game. Afterwards, I started playing much better." (dpa)