Andy Murray and Rafael Nadal win opening ATP World Tour Finals matches

Andy Murray began his ATP World Tour Finals campaign with a convincing win over Spain's David Ferrer in London.

The Briton, 28, won 6-4 6-4 at the O2 Arena and will next play Rafael Nadal, who brushed aside Stan Wawrinka 6-3 6-2 in the day's second round-robin match.

Another victory on Wednesday would ensure Murray ends the year as world number two for the first time.

The Scot's season will continue next week as Great Britain take on Belgium in the Davis Cup final.

"It was a tough match with a lot of long rallies," said Murray. "He fought hard right to the end and made it extremely difficult.

"He didn't serve as well as he can and I played a bit better at the end of both sets, and that got me the win."

Murray makes switch from clay

Murray is always well supported when he plays in London

After some uncertainty over whether Murray would sacrifice his place in London to remain healthy for the showpiece in Belgium on 27-29 November, the Scot was in committed mood once he stepped out into the O2 Arena for his first round-robin match.

He spent several days last week practising on clay for Britain's first Davis Cup final since 1978, but there was little sign of rustiness on the switch back to an indoor hard court.

Four break points slipped by in the first eight games before Murray finally broke through, thanks to a fine volley and a Ferrer double fault.

The seventh seed, 33, was misfiring, making just 47% of first serves, and he was thankful for a loose Murray service game at the start of the second set.

Ferrer was soon battling to keep Murray at bay once again, however, succumbing in game six as the Scot levelled.

Serving to stay in the match, an eighth double fault saw Ferrer go 0-30 down. Then presented with a first match point a bouncing Murray leapt to put away a smash at the second attempt.

The victory gives him an early lead in Group Ilie Nastase, with two players to qualify for the semi-finals on Saturday.

What the pundits said

Murray posed for pictures and signed autographs after his victory

Former British number one Tim Henman: "A straight-sets win against the world number seven is very good, but to compete against the best players there are too many peaks and troughs in his intensity and level of play.

"When he starts talking to his box, he's not focused on the next point and then he's giving the opponent the chance to be the proactive one dictating play."

BBC Sport tennis commentator Andrew Castle: "Apart from one lapse of concentration that lasted 10 or 15 minutes that was a very impressive performance from Andy Murray. There weren't any real dramas but he had to focus hard in the second set to get the job done."

Nadal punishes off-key Wawrinka

Nadal has reached two finals but has yet to win the end-of-season title

Recent history favoured Wawrinka over Nadal, with the Swiss winning three of their past four matches and replacing the Spaniard as French Open champion in June, but his form and mood fell away dramatically on Monday evening.

Wawrinka, seeded fourth, made the perfect start with a break of serve to love but handed the initiative straight back in similar fashion, and looked increasingly frustrated as the evening wore on.

He fired a forehand long to drop serve again in a lengthy eighth game and, after Nadal had wrapped up the set, Wawrinka clung on through six break points at the start of the second.

It did not signal a stiffening of his resolve though, a double fault handing over the break in game three and Wawrinka took out his frustration on the umpire at the changeover.

Fifth seed Nadal has shown encouraging form in recent months and, with his forehand showing its familiar bite off the slow surface, he reeled off nine of the last 11 games to clinch victory.

"Last year was tough," said Nadal, who missed the 2014 tournament following appendicitis. "I'm very happy to start like this, that's important for my confidence. The last couple of weeks I've been playing well."

Wawrinka said: "It was just a really bad day at the office. When something went wrong today, everything went wrong. Just everything went the wrong way. Simple."

Wawrinka threw his racquet as his frustrations got the better of him at one point