O'Donovans dig deep in Lucerne
The O'Donovan brothers had a tough start to the Lucerne Regatta as a disappointing heat forced them into the repechages, where they duly qualified for semi-finals.
Glorious sunshine bathed the Rotsee where the athletes faced uncomfortably warm conditions on the water.
But the Skibbereen men faced heat of a different kind in their first race, where the Greek double of Ninos Nikolaidis and Eleftherios Konsolas led from start to finish.
The Czech duo of Jiri Simanek and Miroslav Vrastil hung on to the Greeks' lead to halfway, where they upped their game to stave off the expected sprint from the O'Donovans in third.
The Olympic silver medallists jacked the rate up to 40 strokes a minute to get back on terms with the leaders, but ran out of water.
"They just left themselves with too much to do," said their coach, Dominic Casey, afterwards.
Ireland's lightweights made certain of qualification later when a top-three placing would have seen them safe.
Only in the last 500 metres did the O'Donovans turn on their legendary sprint, moving through the field to take first place ahead of the fast-finishing Danes, with Russia squeezing through in third.
For the Olympic champions from France, it was very much business as usual as Pierre Houin and Jeremie Azou, cruised to a comfortable win in their heat.
In the open-weight women's single sculls, Sanita Puspure and Monika Dukarska both finished second in their respective heats to qualify for the quarter-finals.
Puspure really found her form then, leading the field across the line in the fastest time of the afternoon. Dukarska also qualified for the semi-finals by finishing third in her race.
Mark and O'Donovan and Shane O'Driscoll will bid to make it four golds in a row in the lightweight men's pair tomorrow, with only a straight final needed to determine the honours.
Lightweight single sculler Denise Walsh was pulled out of the competition before the draw took place. "She's had a lot of races recently so we're giving her a bit of a break," said Casey.