Novak Djokovic boosted his chances of keeping his world No3 ranking from Andy Murray with an impressive display at the Sony Ericsson Open in Miami.

The Serb showed a return to form as he beat Jo-Wilfried Tsonga 63, 64 to set up a semi-final against Roger Federer tomorrow.

Djokovic delivered dashing groundstrokes and generated plenty of spin on his second serves to see off the player he beat to win the Australian Open last year.

The 21-year-old will drop to No4 in the rankings if he fails to beat Federer and then Murray, who plays in the quarter-finals later today, goes on to win the tournament.

Djokovic is only focusing on his match and said: "With Roger, there's not much to say about him. He's so consistent in the major events. He's been so dominant the last couple of years. It is going to be a tough, tough encounter".

Federer ignored the partisan home crowd to defeat American Andy Roddick 6-3, 4-6, 6-4.

Roddick struggled against the Swiss star's first serve in the opening set and was broken twice. The second set was a different story, though, after Federer double-faulted on break point for a 4-3 lead.

The American served for the set at 5-4 and Federer had a chance to break but in the end a long return on a serve secured Roddick a third set.

In a tight deciding set, dominated by serve with the first four games won to love, a stroke of luck set up Federer for the match point.

Roddick was a point away from squaring the match at 5-5 but Federer's backhand pass attempt clipped the net and looped over the forlorn American.

A smart backhand pass then gave Federer a 17th win in 19 meetings with Roddick.

"I should have had it under control in the second set," said Federer. "I lost that and was under quite a bit of pressure in the third set. So I'm happy I got through it.

"I got maybe a touch lucky at that passing shot. But, I mean, I hit it well and came up with a great shot and match point."

Murray, meanwhile, faces Fernando Verdasco, the player who knocked him out of the Australian Open.

The Briton had beaten the big-hitting Spaniard in all their five previous meetings but Verdasco, given new belief by his role in helping Spain win the Davis Cup, turned the tables.