Luke Plapp has had to give up the race lead at Paris-Nice despite giving everything in a noble defence of the yellow jersey that earned the Australian champion plenty of plaudits.

Sean Kelly, record seven-time winner of the iconic week-long French race, was among those to salute Plapp's exhausting efforts to try to retain the jersey in Friday's 198.2km sixth stage.

But after finishing a weary 11th following the steep slog up La Colle sur Loup, Plapp, who dropped from first to third in the general classification now 34 seconds behind new US leader Brandon McNulty, admitted he had emptied the tank.

"Look, that was all I had. I crossed the finish line empty, and I think I limited my losses as much as I could - and I'm still there on the podium," said Plapp.

"It was a privilege to be in yellow," added the 23-year-old as he reflected on wearing the jersey that's been won in the past by a host of the sport's legends like Tour de France winners Jacques Anquetil, Eddy Merckx, Miguel Indurain and last year's winner, Tadej Pogacar.

Plapp had decided to try to stay with race favourite Remco Evenepoel, recognising the 2022 world champion as the major threat, but up ahead, a breakaway trio, featuring two Americans, McNulty and Matteo Jorgenson, and eventual stage winner, Denmark's Mattias Skjelmose, stole a march on the final climb.

Working beautifully together, they opened up a 52-second gap at the finish, with McNulty, backed by the powerful Team UAE Emirates, taking a 23-second lead over Team Visma-Lease a Bike's Jorgenson.

Evenepoel's late burst, which saw him head the chasers just a second clear of Plapp, leaves him fifth at 63 seconds down.

"I still thought we'd be able to bring the three (breakaway) riders back, there was such a long way to the finish, and I thought (Primoz) Roglic and Remco would bring it back," shrugged Plapp.

"But to be honest, I had no legs left anyway, so it was lucky I didn't chase or or try to ride with him (Evenepoel) because at the end I was holding on for dear life just to cross the finish line.

"That was probably as hard a day as it gets for me, it's the furthest thing from a time trialist's sort of climb.

"Hopefully, tomorrow, we can look for some redemption there. With the time gap there, Remco still has to race quite hard, so do the other guys, so I'm hoping I can just be a passenger and let the race unfold a bit and try benefit from that."

All-time great Kelly, commentating on Eurosport, was hugely impressed by Plapp's performance.

"He's done a real good ride in this company," said the Irishman. "Over this sort of dangerous, technical terrain on slippery roads for quite a time, he's defended the jersey very well. Tactically, he's going to learn a lot for this too."

Snow is forecast for the penultimate stage to Auron on Saturday, with race organisers reducing the stage to 104km while retaining a demanding final 15.3km climb with a 5.7 per cent average gradient.

"It's the right decision, it risked being too dangerous and too extreme," said Evenepoel.