Great Britain sculler Alan Campbell could not repeat his Henley heroics of Saturday, suffering a three-length defeat by New Zealand's Mahe Drysdale.
Campbell, clearly struggling after beating Olympic champion Olaf Tufte, went down early in Sunday's final.
"He's set the standard and I'll have to find a way to beat him," said Campbell.
GB also lost in the men's double sculls but there were elite wins in the men's and women's eights, men's fours and women's quads at the Royal Regatta.
In a thrilling final in the blue riband Grand Challenge Cup, the GB men's eight conceded an early lead and went neck-and-neck down the course with a US squad crew from Princeton and California.
But the home crew took advantage of the Henley course, which is 112 metres longer than international standard, to pull ahead in front of a roaring home crowd and win by a length.
In a blustery headwind and choppy water, Olympic bronze medallist Drysdale looked supreme in winning the Diamond Challenge Sculls for the second time, inflicting twice-champion Campbell's first Henley singles loss in 12 races.
"Maybe if I'd had a lighter race yesterday I would have had more juice in the tank"
Campbell billed the event as the competition to find the best match-racer in the world, and only Czech silver-medallist Ondrej Synek was missing of the top-five finishers in the 2008 Olympics.
Racing for Tideway Scullers School, the Chiswick club where Drysdale often trains during the winter, Campbell struggled with the wind on the start and was down from there.
But Drysdale, who was below his best at the Beijing Olympics because of a virus, has given notice with his form of his intention to win a fourth world title in Poland in August.
The duo will not meet again until then as Campbell has opted to miss next weekend's World Cup regatta in Lucerne.
"Maybe if I'd had a lighter race yesterday I would have had more juice in the tank," Campbell admitted.
"I'm confident he's beatable but he's in fantastic form and in some ways he's stronger than before the Olympic Games.
"He's shown he's the best match-racer of the lot of us but I had a brilliant race yesterday and I hope I'll be remembered for that."
In the double sculls, British duo Matthew Wells and Stephen Rowbotham again failed to match Matthew Trott and Nathan Cohen, who finished two places ahead of them in second place in the last World Cup event in Munich.
The final verdict of a length to the Kiwis had been more for much of the race, until they struggled with their steering.
MARTIN GOUGH BLOG"We don't know if the New Zealand squad have something more than us at the moment or if it is us but from the 300m to the 1,000m mark they took us," Rowbotham admitted.
"We have three days until Lucerne and we thought we would have a chance here to put a marker down. Despite losing we still think we can win there."
But the new-look GB women's quadruple scull of Katie Greves, Sarah Cowburn, Beth Rodford and Rosamund Bradbury defeated their New Zealand counterparts for the second time in a fortnight.
Great Britain's women's eight, in a line-up featuring the recently retired Sarah Winckless, out-paced an impressive Yale University crew in the Remenham Challenge Cup.
The GB men's four - featuring three men with silver medals from the Olympic eight - won with ease from New Zealand's lightweights, with the verdict three-and-a-half lengths.
Poland's Olympic champion men's quad mistakenly stopped just before the finish line but had done enough to ensure victory over a young GB crew, who have run them close this season.
And New Zealand's pair of Eric Murray and Hamish Bond, who conquered GB duo Peter Reed and Andy Hodge in the semi-finals, beat the South African holders of the Silver Goblets.
Shaun Keeling and Ramon DiClemente were fifth in the Olympic final but lost easily to Murray and Bond, half of the NZ four who could not reach the final in Beijing.
Results:
Temple (student eights) Princeton Univ, USA beat Brown Univ, USA by ¾ length
Wyfold (club coxless fours) Sydney RC, AUS beat Nottingham & Union RC by 1 ¾ lengths
Princess Royal (women's single sculls) E. Twigg, NZ beat G.L. Stone, USA by 2 ¼ lengths
Ladies' Plate (intermediate eights) Brown Univ 'A', USA beat Leander Club & Molesey BC (GB U23s) by ½ length
Britannia (club coxed fours) Agecroft RC (Manchester) beat Vesta RC (London) by ¾ length
Goblets (pairs) E. Murray & H. Bond, NZ beat S.B. Keeling & R.P. Di Clementé, RSA easily
Princess Elizabeth (school/junior eights) Eton College beat Abingdon School by five lengths
Prince of Wales (intermediate quad sculls) Durham Univ & Oxford Brookes Univ beat Leander Club by two lengths
Stewards (elite coxless fours) Leander Club & Reading Univ (Great Britain) beat Waiariki RC, (NZ lightweights) by 3 ½ lengths
Remenham (women's eights) Leander Club & Wallingford RC (Great Britain) beat Yale Univ, USA by 3 lengths
Visitors (intermediate coxless fours) Isis BC (Oxford Univ) beat Mercyhurst College, USA by 3 ½ lengths
Queen Mother (elite quad sculls) A.Z.S. Szczecin & A.Z.S. Gorzow (Poland) beat Reading Univ & Leander Club (Great Britain) by ¾ length
Diamonds (single sculls) M. Drysdale, NZ beat A.W. Campbell, GB by 3 lengths
Thames (club eights) Molesey BC 'A' beat Henley RC by 1 ½ lengths
Princess Grace (women's quad sculls) Leander Club & Westminster School (Great Britain) beat Waiariki RC 'A' (New Zealand) by 3 lengths
Grand (elite eights) Leander Club & Molesey BC (Great Britain) beat Princeton TC & California RC, USA by 1 length
Double Sculls M.C. Trott & N. Cohen, NZ beat M.W. Wells & S.C. Rowbotham, GB by 1 length
Prince Albert (student coxed fours) Oxford Brookes Univ beat Yale Univ, USA easily
Fawley (school quad sculls) Westminster School beat Melbourne Grammar School, AUS by 2/3 length
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