“Avant garde” is one of those phrases nearly impossible to say without feeling at least a little pretentious. It must be said, however, that the UC Berkeley Symphony Orchestra ushered in the new concert season with a taste of the avant garde.

Performing symphonies by Jean Sibelius, Cindy Cox and Pyotr Tchaikovsky, the UC Berkeley Symphony Orchestra opened the season Oct. 2 through 4 in Hertz Hall with pieces distinct in their innovative compositional methods.

The concert began with the dramatic opening scale of Jean Sibelius’ “Symphony No. 7 in C Major,” a single-movement symphony consisting of four distinct sections. As Sibelius’ final published symphony, the piece defies the standard four-movement symphonic structure, instead evolving organically through four distinct sections united by repeated themes.

Growing from the expository Adagio section, the symphony covers an expansive emotional landscape, ranging from the soaring passages of the Adagio to the more playful, staccato lines in the following Vivacissimo section, culminating in a return to the expansive and dramatic in the final section. Led by conductor David Milnes, the orchestra did a remarkable job tracing the churning moods of the piece, transitioning seamlessly between darker and lighter passages.

“Las Aguas del Sur,” written by the new UC Berkeley music department chair, Cindy Cox, contrasted refreshingly with the Sibelius. Described as post-tonal, Cox’s piece is lyrical, but not melodic in the traditional sense; instead, it conveys a sense of motion through rhythm and incorporates various experimental playing techniques such as the “seagull,” an eerie, high-pitched gliding sound string players produce by sliding their fingers down the strings of their instruments. Though nontraditional and atonal, the piece is atmospheric, emotionally rich and, according to Cox, written to be evocative of the other-worldly.

“The Cindy Cox piece is a brand new piece written for us a couple of years ago, and the Sibelius seemed like it would go well with that because it’s a nature piece — it’s north and Cindy Cox’s is the southern tip of Argentina,” Milnes explained to The Daily Californian in an interview. “One of the reasons we have a reputation for doing so well with new music is the players put themselves into it. It doesn’t matter what the piece is or if you haven’t heard anything like it if the players are communicating through the music. It’s like speaking a language.”

The program closed with Pyotr Tchaikovsky’s “Symphony No. 6 in B Minor, ‘Pathetique,’ ” Tchaikovsky’s last published work. Like the Sibelius, the approach to the symphonic form was groundbreaking at the time; the manner of ending the symphony in Adagio lamentoso rather than on a more triumphant, dramatic note was later taken up by other composers as a solution to the rigidity of the symphonic form.

Though the first movement begins on a dark note, the energy and mood quickly pick up and give way to dramatic, lush passages, characterized by long melodic line. The inner movements, Allegro con grazia — quickly, with grace — and Allegro molto vivace — quickly, more vivacious — are simpler and more energetic, and the final movement, the Adagio, is slow and mournful. Over the course of the piece, the orchestra covered a dynamic emotional range with a delicacy and expertise that brought the concert to a satisfying and moving conclusion.

UC Berkeley Symphony Orchestra’s next performance is on Oct. 31 at 8 p.m.