St. Lawrence String Quartet. (Eric Cheng)

The St. Lawrence Quartet that appeared at the Kreeger Museum was not the same group that appeared there during the museum’s first concert season nearly 20 years ago. It wasn’t just that two of the players are different (the cellist, Christopher Costanza, and the second violinist, Mark Fewer, joined the group in 2003 and 2014, respectively). It’s also that, on Friday, the group did not show the same clean virtuosity that it used to show when I first heard them in the early 2000s. The searing energy is still there, and these days the reputation precedes it, but on Friday, neither was fully backed up by the performance.

Classical sonata form is known for juxtaposing two contrasting themes and exploring the interplay between them. The program did this in its own fashion — thematically. The first theme was classical quartet form, represented by the first of Haydn’s seminal Op. 20 quartets, the one in E-flat, offered with plenty of verve and a number of small imprecisions. The second theme was opera, represented by Giuseppe Verdi, whose lone string quartet — written during an enforced break in rehearsals for a production of “Aida,” and rife with melody that evoked his operas — finished the program. And the two themes met in the powerful second quartet by Benjamin Britten, a composer known for opera but also proficient in other forms; this piece was the literal and figurative heart of the evening.

Geoff Nuttall, the first violinist, gave engaging spoken introductions before the group plunged headlong into each work, underlining the sense of intimacy given by a room that felt and sounded smaller than its generous dimensions, with acoustic properties — governed by the arcs of the vaulted ceiling — that magnified slight impurities of sound. Perhaps partly as a result, the playing felt loose-limbed and a little blowsy; the repetitions in the second-movement minuet in the Haydn feeling dutiful, the ends of movements sometimes trailing off inconclusively.

That is not to say there wasn’t some fine playing, among others from the violist Lesley Robertson. Costanza veered the furthest between extremes, sounding sometimes coarse and strident in the Haydn, singing mellifluously in the Verdi, and offering, in his cadenza in the final movement of the Britten, some of the best playing of the night.

That movement was arguably the strongest musical moment of the night in any case. The Britten second quartet is an assured, vital work in three movements, culminating in an extended chaconne or “Chacony,” the spelling presumably a nod to Henry Purcell — the piece was written to commemorate the 250th anniversary of his death. The Chacony unfolds in a sequence of 21 variations presented in sets interspersed with solo interludes for individual instruments: dramatic playing harnessed by a system that worked. It epitomized the evening’s message, even if the evening itself was not the St. Lawrence’s strongest moment.