By Peter Smith

WEYMOUTH, England (Reuters) - Red-headed Dane Jonas Hogh-Christensen underlined his threat to Ben Ainslie's bid for a fourth consecutive Olympic gold when he maintained a healthy lead over the Briton in the Finn dinghy on Tuesday.

Hogh-Christensen continued his inspired form in Weymouth with a first and second in race's five and six of the regatta to establish a 10-point lead over second-placed Ainslie.

Christensen, 31, said he had been sailing his best over the past three days.

"I've always had a feeling I can beat Ben on my best day, and all the other guys," he told reporters. "I'm a bit surprised it's going this well."

Ainslie, Olympic champion in the Laser dinghy in 2004 and the heavier Finn dinghy in 2004 and 2008, was fourth and second on Tuesday.

The downbeat Briton said: "It's not really working out and is a difficult place (for me) to be. But with 10 points it's still on."

There are four races remaining before the medal race when points count double.

Wednesday is a rest day when Ainslie said he would spend time with the physio and "eat plenty". Christensen has a weight advantage over the British helmsman in a class which is for heavyweights.

The Star class is shaping up into a fascinating battle with reigning champions Iain Percy and Andrew Simpson holding a four-point advantage over Brazilians Robert Scheidt and Bruno Prada after six races.

"We are definitely here to defend our title but it is going to be a fight to the end," said Percy after the British pair finished first ahead of the Brazilians in race five, then saw the positions reversed in race six.

Ireland's Annalise Murphy's stunning opening to the regatta continued when she won her fourth Laser Radial race out of four.

An elated Murphy, who described her performance as "brilliant, can't get much better than winning the first four races", is following her mother Cathy McAleavey in Olympic sailing.

McAleavy competed in the Seoul Olympics in 1988 but the tall Murphy is on course to far exceed her mother's achievements.

With only four points from four races she has a lead of 12 over her nearest rival Belgium's Evi Van Ecker and 14 points ahead of Dutch sailor Marit Bouwmeester. British hope Alison Young was second in each race to move up to fourth overall.

Australia's 2012 world champions Nathan Outteridge and Iain Jensen consolidated their lead to nine points over antipodean rivals New Zealand in the 49er skiff.

The New Zealand team of Peter Burling and Blair Tuke, sailing together at the Olympics for the first time, won the first of two races on Tuesday but could only manage seventh in the second.

Windsurfers got on the water for the first time in what may well be the swansong for this class at the Olympics. The RS.X class for men and women is being replaced by a kiteboarding class at the Rio de Janeiro Olympic Games in 2016.

Dutch 2011 world champion Dorian van Rijsselberge laid down the gauntlet to his rivals when he won both the day's races. In an unusual twist, Rijsselberge led home Pole Przemyslaw Miarczynski and Germany's Toni Wilhelm in both races.

Miarczynski was delighted with his start to the regatta after a bad start in the second race in waves up to one meter or more with the swell.

The women windsurfers also completed their first two races of 10 on Tuesday with Spain's Marina Alabau Neira vying with Israel's world champion Lee-El Korzits for early supremacy.

(Editing by Justin Palmer)