Ben O'Connor made it an Australian treble at the Volta a Catalunya on Wednesday when he soared to victory on the third stage in the Pyrenees.

Victory for the AG2R climber follows wins for Australians on stage 1 with Michael Matthews and stage 2, won by sprinter Kaden Groves.

The third stage was a 161km mountain run from the French coastal city of Perpignan to the Pyrenean ski resort of La Molina with the second climb hitting 1800m altitude.

O'Connor broke for victory alone on the final climb and just about hung on as a clutch of pretenders to the title reeled him to within six seconds.

The 19-year-old Spanish climber Juan Ayuso of the UAE Emirates team came second with Nairo Quintana third.

O'Connor holds the overall lead going into stage four with a 10sec edge on Ayuso and 12sec over Quintana.

"There was a strong headwind on the final climb but O'Connor really timed it well," UAE's Spanish rookie said.

"We came close to catching him but my legs are good and we'll have another shot tomorrow," he said.

Bike Exchange captain Simon Yates crashed and said his overall title effort, and even the possibility of a stage win, were now compromised.

Thursday's fourth stage is also a mountain run to the Boi Taull ski station with three category 1 climbs on the agenda.

Meanwhile, Italy's Sonny Colbrelli, who suffered cardio-respiratory arrest after stage 1, was described as lucky to be alive by one of the race doctors who treated him.

"If he had suffered a heart attack while training without a defribulator around, Colbrelli could have died," race doctor Alex Flor Costa told Spanish press.

First aid staff, who revived the rider at the finish line in the seaside town of Sant Feliu de Guixols on Monday performed emergency CPR cardiac methods and used a defibrillator.

The Bahrain-Victorious rider remains in hospital in Girona after it was confirmed he had suffered an unstable cardiac arrhythmia that saw him suffer convulsions and loss of consciousness.