America's Pacifica Quartet has just completed a six city tour of Australia courtesy of the country's stalwart chamber music promoter, Musica Viva. One part of the deal with MV is invariably the inclusion of an Australian composition in any international tourist's program – in this case Nigel Westlake's String Quartet no. 2 – hoping that it will become part of the group's future repertoire. Given that violinist Sibbi Bernhardsson described the work as “magnificent” in his introduction, this looks likely when the Pacificas return to their Indiana base. But the key message that came across from their programme was the natural feeling they have for the works of Shostakovich.

Culminating their Sydney concert with the Russian's Third Quartet from 1946, all of the theatricality that they'd been revealing in their whole-hearted attack upon Westlake's persuasive discords and their dramatic pauses in Beethoven's last quartet, it seemed only right that their Shostakovich went from a superfast Allegretto to a pin-drop introduction of the second movement's twisted waltz, to a furious Allegro, and then to the Adagio's desolate lament where all four players had their moment in the sun in a movement that seemed to have been written for the spirit of the Pacificas.

They may even have answered Beethoven's Eternal Question, borrowed by Shostakovich as the motto for his fifth movement. For, as an ensemble, they sensitively avoided the potential for schmaltz that lies within it, then, guided by the delicate precision of leader Simin Ganatra's final harmonics, they almost took their audience off the audibility charts into blissful silence. But then Beethoven may have been toying with us when he posed the question, “Must it be?” on the score of the last movement of his Op.135 quartet. Was he being philosophical about his imminent death, or was he admitting to his publisher that he was finding great difficulty in composing it? In some performances it certainly sounds a more reluctant effort than the vast majority of the master's creations. But the Pacificas were persuasive even here – a Zen viola lead-in from Masumi Per Rostad, thrilling attack on the Grave's sequence of chords, and joy in the Dvořákian folksiness that smiles through this last, perhaps weary effort.

Nothing folksy in the Westlake, whose musical language is described by the composer as “simply based on the building of musical resonances, melodic contours and rhythmic impetus”. Nothing simple about this 24-minute work. As with the Shostakovich, the Pacficas found their greatest empathy in a very slow and sustained third movement – virtually a violin solo over percussive beats at its beginning, it then builds intensity through cross-string work by Brandon Vamos' cello and Per Rostad's viola, before fading to an intentional irresolution. Throughout, much is based on the pairing of instruments differently – a tennis match between lead violin and viola in the first movement, the two violins as a team in the second, and first violin and cello mirroring each other's phrases in the fourth. As with the Shostakovich, the work ends with Ganatra's instrument soaring into the stratosphere; but behind her this time is a feverish scherzo, threatening to plunge the musicians into mayhem.

However, the Pacificas convinced us that they were still in control of a work that had also convinced them of its musical validity.