On 17 August 1989 the first Qantas 747-400, VH-OJA 'City of Canberra', touched down at Sydney Airport after a non-stop flight from London to Sydney. The 18,001km flight, under the command of Captain David Massy-Greene, took 20 hours, nine minutes and five seconds
To be fair, an excellent and well planned effort. But if I recall, it had special cooled fuel and was topped up with minimal fuel used to taxi, virtually no load and stripped out of unnecessary weight (even low water supplies for the very few special passengers). Not really a representative operation, but a good illustration of capability.