O’Connor, who finished fourth at last year's Tour, earned third place overall in the south-east France stage race that acts as a key dress rehearsal for the world's biggest race.
Yet while Perth local’s performance was highly encouraging with the grand tour less than three weeks away, he was still no match for the race winner Roglič and his Jumbo-Visma teammate, runner-up Jonas Vingegaard.
O'Connor, lying third overnight, again finished third on Sunday's eighth and final stage, a mountainous 138.8km route from Saint-Alban-Leysse to Plateau de Salaison.
But he was again no match for one of the Tour favourites Roglic, and his powerful Danish right-hand man Vingegaard, who powered away from the rest of the field on the final climb.
Once they'd broken their opponents, with their nearest challenger O'Connor 15 seconds adrift, the teammates celebrated hand in hand as they crossed the finish line.
Roglič was happy to push Vingegaard forward, allowing him to take the stage and finish second in the overall standings, while he claimed the overall victory by 40 seconds from the Dane and 1:41 ahead of AG2R Citroen's O'Connor.
"I finally won some races in France so it's super nice," said Roglič, who famously just missed out at the 2020 Tour de France, losing to his compatriot Tadej Pogacar in the climax, and had to abandon last year's race after a crash.
“Jonas (who finished second in last year's Tour) was super strong on the last climb and it's crazy, an incredible day for our team.
"As you can see, things are going in the right direction so we can be confident. We have some more time, some more work to do and should be ready for the Tour."
Another Australian Jack Haig, of Bahrain-Victorious, also completed an excellent race, finishing fifth overall at 3:13 down on Roglic.
But he was quick to accept that both Roglič and Vingegaard had laid down a marker as the major threats to Pogacar's bid for a third straight Tour title.
Roglič has won the past three Spanish Vuelta titles but the Tour remains his major focus after also winning the celebrated Paris-Nice stage race in March.
