Buoyant Katherine Grainger smashes record out of the water

The prize is tantalisingly close, but Katherine Grainger has suffered too many disappointments to believe just yet that an Olympic gold medal is hers.

Three silvers would be a haul with which some athletes would be satisfied. Not Grainger, who finished second in Sydney, Athens and Beijing and now, at 36, she will make another push for the top spot of the podium in Friday's final of the women's double sculls.

The signs are good. Grainger and her partner, Anna Watkins, cruised through their heat, posting a time of 6min 44.33sec, which broke the Olympic record by more than five seconds. The Australian pair of Kim Crow and Brooke Pratley are expected to be stern challengers – they were just over four seconds slower than Great Britain in winning their own heat.

"I think I will be exploding on Friday if it goes well," smiled Grainger. "That had to be one of the best days I've experienced in rowing, and it was only a heat.

"It was so satisfying putting in a good performance in a home Olympics, in front of a home crowd. This is the one we want more than anything. From any of my Olympic experiences before, this is the important one."

Watkins and Grainger were both dazzled by the raucous support of the home crowd – "Now I can understand what it must feel like to be a footballer," Watkins said – and they are confident that they have plenty in reserve, their daunting time yesterday notwithstanding.

"Mentally, we could not be in a better place," Watkins continued. "We know there is more to come and we know how to get it out of ourselves. We didn't want to show it all in the heat."

The performance of Grainger and Watkins was the highlight of a heartening day for Great Britain. In the women's quadruple sculls, Team GB recovered from last place at the halfway mark in their repêchage to qualify for tomorrow's final, while the men's eight – including 1992 gold medallist Greg Searle – won their repêchage ahead of Olympic champions Canada to reach the race for medals, also tomorrow.

The men's four, three members of which won gold in Beijing four years ago, qualified for the semi-finals, although the Australian boat outshone them in yesterday's heats by setting a new Olympic record of 5:47.06. Great Britain won the second heat with ease but were more than three seconds slower.

As long as both boats negotiate the semi-finals on Thursday, Saturday's final could be one of the closest of the regatta, while the United States crew cannot be discounted, either.

"You could argue that Australia are favourites at the moment," said Tom James, triumphant in the men's four in Beijing. "But you row to have tough racing. If you win, it feels more memorable."

Drew Ginn is chasing his fourth Olympic gold for Australia, who believe Great Britain are scared of them. Ginn added: "Any time you take it to people, there is fear and anxiety. We are prepared for the hardest battle."

Missing the boat? Grainger's Games record

Sydney 2000 In her first Olympic Games, Grainger and the women's four advanced to the finals, posting the second-fastest time in the repêchage round. Great Britain came up short of the gold medal, placed a full two seconds behind Germany to claim silver.

Athens 2004 History repeated itself in for Grainger in the coxless pairs. She and Cath Bishop posted the fastest time in the repêchage, but she was disappointed yet again, finishing with silver two seconds behind Romania.

Beijing 2008 Surging through with the fastest time in heat two of women's quad sculls, Grainger and her team had gold within grasp for most of the race before China surpassed them 500m from the finish. NICK FROST