The Portland String Quartet is taking a well-deserved victory lap this season, celebrating its 50th anniversary by revisiting some of the quartet repertory’s greatest works.

For the second concert in the series, the players – violinist Ronald Lantz and violist Julia Adams, who have played with the quartet from the start; violinist Dean Stein, who joined in 2013, and cellist Andrew Mark, who joined this year – set their sights on Bartók, Mozart and Brahms, composers whose music is at the core of the European repertory.

Actually, though, it’s worth noting that when the quartet started, Bartók’s six quartets were still outliers – important works, in many musicians’ estimation, but still considered daunting by many listeners. The first complete recorded traversal of the set (by the Juilliard String Quartet) had been released less than 20 years before the Portland String Quartet played its first concert, and was considered a daring feat.

Hardly anyone finds Bartók scary any more, and in any case, his String Quartet No. 1 (Op. 7), which opened Sunday’s concert, is now 109 years old. The comparatively conservative start of a journey that took him into greater complexities and dissonances in the three decades that followed, it has a melancholy, at times even dour, spirit. But it is also full of interesting contrapuntal techniques and internal dialogues between the instruments, both individually and in varied groups.

The ensemble put a clarifying spotlight on those elements, but more crucially, it closely followed the score’s almost constantly shifting levels of intensity and internal tension, in a taut reading that never loosened its grip.

Mozart’s String Quartet in A major (K. 464) filled out the first half of the program, and it seemed, at first, as if this vigorous score was meant as a palate cleanser, a return to the cheerful, comfortably familiar language of the late 18th century (it was composed in 1785) after a long immersion in early 20th century angst.

But the Mozart has its transgressive undercurrents as well. One of the six quartets that Mozart dedicated to Haydn, his older contemporary (and predecessor in claiming his creative independence, within the system of aristocratic patronage), the piece moves easily between courtly propriety and assertiveness, with a playful veneer that disguises its rebellious side.

As in the Bartók, the Portland players kept all those elements in focus, but even if you preferred not to ponder the socio-musical politics of the time, the performance was lively, fresh, bright-hued and comfortably paced, even in the brisk finale.

The second half of the program was devoted to Brahms’ String Quartet in A minor (Op. 51, No. 2). In a way, it offered a middle ground between the Mozart and Bartók works, in the sense that it is couched in a familiar harmonic language and includes a hint of courtliness (in its Quasi Menuetto movement), but also embraces the darker coloration and the sense of emotional drama, if not quite the same level of anxiety, that drives Bartók’s score.

The performance was energized and thoughtful, with sharply drawn contrasts and the rich, warm tone that characterizes this quartet at its best.

Allan Kozinn is a former music critic and culture writer for The New York Times who lives in Portland. He can be contacted at:

allankozinn@gmail.com

Twitter: kozinn