Who are the great symphonists of the 20th century? Sibelius and Mahler? Unquestionably. Prokofiev and Shostakovich? Debatable. Ralph Vaughan Williams? Indubitably.

If you live on this side of the pond, however, you are probably not aware of the latter’s amazing body of work. Vaughan Williams composed nine symphonies, none of which are performed on a regular basis in the United States. In a very real sense, he was the voice of his generation, from the gloriously patriotic (Symphonies Nos.1 & 2),through the pastoral movement (No. 3), into the years when civilization itself seemed on the verge of collapse (Nos. 4 & 6).

This is, relatively speaking, a big year in New York for Vaughan Williams. Leon Botstein will conduct the fourth symphony in April, and on Sunday afternoon, Sir Colin Davis led the forces of the London Symphony in the powerful sixth.

This being the first week of October, there is probably not a lot of cachet in declaring Sunday’s the finest orchestral performance of the season thus far, but I have the feeling I will still be stating this in May. It is the inevitable consequence of international travel that the third performance by a European orchestra in New York is usually the best, once the jet lag has worn off. This certainly was the case Sunday: The glittering LSO was close to perfect.

Sir Colin captured the intensity of the piece right from the opening, unleashing his superb lower brass for maximum impact. The pacing was inexorable, the otherworldly solos by the saxophone downright spiritual, the needle-sharp entrances and well-coordinated exits spot-on. Performing the work without pause between the movements also increased the tension, which was only broken in the dreamlike ending section (think Holst’s “The Planets”). The scherzo, described by the composer’s wife Ursula as “clear as ice,” was especially thrilling.

The next piece on the program was William Walton’s Symphony No. 1, of which the London Symphony had introduced the first three movements in 1934. On Sunday, the LSO emphasized the gigantic scope of the work: Its sweeping grandiloquence, heavily laden with the trappings of ceremony, is rather like Walton’s more famous score for the Laurence Olivier version of “Henry V.”

The problem was that the Vaughan Williams sixth is a hard act to follow. What VW said in a few measures, Walton expounds for 15 minutes. Only Walton’s third movement, marked Andante con malinconia, can be considered the equal of such high-level British symphonic writing; its Brucknerian build to a throbbing conclusion is quite masterful indeed. If one is going to choose an advocate for this type of music, then Sir Colin has to be the odds-on favorite.

Walton was also especially taken with this slow movement, stating that he had created “something a bit A1 extra.” Come to think of it, that’s an apt description for this concert as a whole.