The AG2R Citröen rider attacked in the final nine kilometres of the 161km stage, which began at Perpignan in France and the peloton back into Spain.

Several general classification contenders sought to close on O'Connor as the final climb of the day continued, but the Australian held on to secure the stage win in a time of 4 hours, 12min, 51sec.

Spain’s Juan Ayuso finished as the runner-up at six seconds down.

Nairo Quintana and Sergio Higuita of Colombia, and Portugal’s Joao Almeida were awarded the same time rounding off the top five.

O'Connor’s success means Australian riders have won the opening three stages of the International Cycling Union (UCI) World Tour race, after Michael Matthews and Kaden Groves.

"I was ill and I had to abandon Paris-Nice which was one of my objectives," O'Connor told AG2R Citröen after the stage.

"I approached this week with confidence because I knew that my form was there.

"Today, I didn't expect to finish alone because I believed that other runners would be able to follow me.

"I decided to try my luck in the finale and it worked."

"It was not necessarily a climb that suited me, I like high mountains," O'Connor added.

"I knew I had to be smart to follow those who would attack.

"I know that the Tour of Catalonia is a tricky race but, with my teammates, I will try to keep this leader's jersey until the end."

O’Connor now leads the race by 10 seconds from second place Ayuso, with Quintana a further two seconds adrift.

Britain’s Simon Yates and the Netherlands’ Tom Dumoulin, who were among the pre-race favourites, both abandoned today due to illness.

The fourth stage will see the riders complete a 166.7 kilometre hilly route from La Seu d'Urgell to Boí Taüll.