Smith won silver in Beijing as part of the men's eights
Great Britain's Olympic rowers swapped muggy Beijing for sleet on the River Thames as they returned to action.
"It was worlds apart, completely different," said silver medallist Colin Smith, rowing with Oxford University at the Head of the River Fours.
Smith's four were 19 seconds behind the top Cambridge boat, who also beat Olympic champion Andy Hodge's crew.
Tideway Scullers School, including Kiwi star Mahe Drysdale and GB single sculler Alan Campbell, won overall.
Drysdale, third in Beijing, and Campbell, who finished fifth, were racing in a quadruple scull - the fastest of the boat types racing in a 6.8km time trial event involving more than 500 crews.
They were nine seconds faster than a Reading University line-up of British under-23 internationals but Cambridge's top coxed four - a far slower boat type - was just 32 seconds behind that.
They beat Hodge's Molesey club crew by 16 seconds and Smith's (called Isis) by 19.
And worryingly for Smith, this year's Oxford president, the second Cambridge boat was not far behind, firing an early shot in the battle between the two universities, who contest the Boat Race on 29 March.
I've no doubt it was a reality check for some of the guys about the environment
GB and Oxford University rower Colin Smith
Smith is just one of several international stars in the Oxford squad this year but they only started rowing together in September and many have not experienced the unique conditions on the Thames course before.
Cambridge have a settled squad, with several young British oarsmen, like Tom Ransley and president Henry Pelly, who will expect to be in Olympic contention in 2012.
"It was a tough day with tough weather but we were already aware of the problems we faced and they've not changed," Smith told BBC Sport.
"Oxford have a new team so we have further to go to get people rowing together. Cambridge are further down that line.
"I've no doubt it was a reality check for some of the guys about the environment we'll have to compete in for the Boat Race."
The university clubs are back on the same course in mid-December, when each has a trial race.
Great Britain's Olympians will now settle back into low-key training until the New Year, when they take part in a series of trials leading up to the first World Cup regatta, starting in Barcelona on 29 May.
Tideway Scullers also produced the fastest women's crew at the Head of the River Fours.
Natasha Howard, who missed the Olympic eights final with illness, joined three foreign internationals to go seven seconds faster than former crew-mate Sarah Winckless in a London RC composite line-up.
Debbie Flood, who broke down in tears when her quad were beaten to gold by China in the Olympic final, won the women's elite coxless fours with her club, Leander.