Mr. Brahms had good company Saturday evening at the Michigan Theater when the Ann Arbor Symphony Orchestra presented “Brahms and Friends,” its second mainstage concert of the season.

Truth be told, there was only one “friend” on this two-composer program - a Northern comrade, Sibelius - but the companionship on stage could not have been better. The orchestra, following on its triumphant all-Beethoven season-opener, was in top form, and in the young pianist Roman Rabinovich, it had a soloist superbly attuned to both the subtle intimacies and extroverted glories of the headlining work, the Brahms Piano Concerto No. 1 in D Minor.

So far this season, under its music director Arie Lipsky, the A2SO has been going for the gold, tackling giant works of the orchestral repertoire. The Beethoven Ninth Symphony was the centerpiece of the opening concert, but the concert preface consisted of several smaller works. Saturday, the pieces on the bill - the Brahms concerto and the Sibelius Symphony No. 2 in D Major - were so grand and so large that only two would fit, one for each half.

And that was one of the terrific things about the program: just two works, worthy of one’s full attention, to digest and appreciate. That they both paint vast canvases and work on a vast scale was only a plus for the concert’s cohesion.

It’s hard to say enough good about the playing Saturday, in both works. The Brahms first: the orchestra’s magisterial, dark-hued opening was remarkable for both its leanness and its warmth, a combination that Lipsky and the players maintained throughout the concerto. And while concerti can be musical battles between soloist and ensemble, this one was a partnership. Solo entrances slipped into the orchestral fabric; the orchestra took up seamlessly where the solos left off. Rabinovich punctuated the orchestra’s statements with chords that rang like exclamations; the orchestra returned the gesture.

Pianist Rabinovich, whom Lipsky has known since Rabinovich was less than a teen, has been here before to play, and let’s hope he’ll return again. His Brahms was full of light and nuance and singing inner voices. What was better? The entrances that whispered with tender intimacy? The shimmering trills? The way he pointed up the tops of phrases? The way he used his hands off the piano, continuing a gesture visually (but never in a showmanlike way) to make a phrase continue to sing in silence? It all added up to a moving - and riveting - performance.

The Sibelius, meanwhile, was hardly content to remain in the “friend of” status. The orchestra and Lipsky - who came out minus his jacket, ready for a workout - were really on, from the downbeat. The opening bars were stunning, wonderfully shaped dynamically and rhythmically. The playing - by strings, by the superb brass, by the winds - was rich and thrilling. And the final movement built and built, perfectly paced, its vistas, underscored by the low strings, growing wider and wider, grander and grander.

That could just be a metaphor for what the A2SO seems to be doing itself this season.