With the 16st 9lb Caspar Ouvaroff giving them considerable ballast in the No. 5 seat, Shiplake took the lead at the barrier, but could not shake off their opponents.
Eton, who had been slightly weakened by a substitution, were never more than half a length adrift and were closing quickly at the line, but Shiplake held on to win by a canvas.
The Diamond Sculls has narrowed to a good field all of similar calibre. Fran Reininger, who was in Oxford's Boat Race winning team at stroke in 1985, overtook Gareth Walters, of Thames Rowing Club, at the half-mile point and held on to a slim lead to win by half a length.
Meanwhile Peter Andersen, a Copenhagen plumber, beat Oleg Kozikov, of the Moscow Institute of Aviation, after passing him at the three-quarter mile mark. Anderson, who represents his coach's employer, the Queensland Amateur Rowing Council, will now race the lightweight John Murphy, of Canada.
In another close race Calman Maclennan, who put a place in the Olympic quadruple scull in jeopardy by rowing for Oxford in this year's Boat Race, was knocked out of the Diamond Challenge Sculls by the German lightweight Sebastian Franke, a winner on both days at the recent Essen regatta.
However, Paul Reedy, of Melbourne University, looks the strongest contender. He won a bronze medal in the double sculls at the 1990 World Championships in Tasmania and a silver in the quadruple sculls in the Los Angeles Olympics.
Only two British scullers remain. Rorie Henderson, of Leander, at the top of the draw, and Robin Williams, of London Rowing Club, at the bottom.
John Wilson, the coach of the Cambridge Boat Race crew, stroked a coxless four from Nottingham County to victory over a Goldie Boat Club four containing the University's present and past two presidents.
Goldie led from the start and held a half-length advantage until half-way up the enclosures when Wilson's crew, made up from lightweights who failed to make the national squad, overtook to win by a length.
In spite of the recent rain, the stream was low enough to allow Trinity College Dublin to set a record for reaching the barrier during the first race of the day. They covered the distance of around 600 metres in 1min 59sec in the Temple Challenge Cup.
Today's racing includes the opening rounds of the Grand Challenge Cup when the South African Olympic eight, entered here as Trident, will meet a strong University of London crew including three former world junior champions.Reuse content