ROTTERDAM, Netherlands (AFP) - Former champions Juan Martin del Potro and Andy Murray showed off improved fitness in first round victories over French opponents on Wednesday at the Rotterdam World Tennis.

Del Potro, the world number four and top seed, tested his delicate left wrist over nearly one and three-quarter hours as he beat Gael Monfils 7-6 (8/6), 6-3.

Murray, a late wild card into the field as he builds strength after his 2013 back operation, dispatched Edouard Roger-Vasselin 6-3, 6-3.

The Scot won the title at the Ahoy stadium in 2009 over Rafael Nadal while Del Potro is defending his 2013 trophy.

Murray finished with 29 winners and broke three times. The win came a week and a half after he led Britain past the US in Davis Cup play in San Diego.

The world number six is playing the event for the fourth time in his bid for a 29th career title.

"I served really well for a set and a half, at the end it's natural that you get a bit nervous, I moved well and made him play the extra ball.

"It got tough at the end and I'm glad I pulled this one off in two sets. I hope to have another good run here this week." Del Potro repeated his win over the flamboyant and crowd-pleasing Monfils from 2013 when he beat the Frenchman in their only other meeting.

Monfils came to the first-round start after winning a title at the weekend and has been beaten in 2014 only by Del Potro and Rafael Nadal in a 12-3 season.

Staying optimistic

Del Potro is recovering from a wrist problem which gave him pain at the Australian Open and sent him to an American specialist last month for consultations and a recovery programme.

"It felt better but I'm still not quite able to hit my backhand as I like," said the South American, who sent last week's Montpellier champion out on a second match point when he drove a forehand winner down the line.

"I'm staying optimistic and trying to keep my mind off of the problem, which is not always easy.

"I'm looking only as far as the next match. I have no pain at the moment and I'm doing my treatment. I hope it feels even better in the next round. I'm very happy to be able to return and try to defend my title." After starting off in somewhat poor humour on Kids day in a noisy stadium, Monfils settled in, matching Del Potro in long rallies and occasionally leaping for an overhead or throwing himself at a passing shot and rolling on the hardcourt.

Del Potro will next play another Frenchman in qualifier Paul-Henri Mathieu.

The Argentine is a huge threat when he's top-seeded: in his last five tournaments at the top of the draw he has lifted five titles and has won 24 matches.

Murray swept through the first set against the 35th-ranked Roger-Vasselin and went up an early break in the second. He will play Austrian Dominic Thiem, who put out Finnish veteran Jarkko Nieminen 6-4, 4-6, 6-4.

Two more seeds fought through to the second round as Frenchman Richard Gasquet, beat Dutchman Thiemo de Bakker 6-7 (5/7), 7-6 (7/2), 6-3 and 35-year-old sixth seed Tommy Haas overcame Spain's Fernando Verdasco, Spain.

Nicolas Mahut of France reached the second round over lucky loser Daniel Brands 7-5, 6-3.