Not even Titus himself would have granted clemency to the New York Philharmonic for what they did to the opening of the overture to “La Clemenza di Tito” on Wednesday evening. The very first note was blown, bowed, and struck at various times, rather than in unison. It matters little whether the timpanist was early or the ensemble late, but I wondered if we were in for another dreadful night at Avery Fisher Hall. Thankfully, the orchestra’s principal guest conductor, Sir Colin Davis, simply would not let that happen.

Two distinguished guest artists aided him in his efforts.The Finnish soprano Soile Isokoski was on hand for a strong presentation of the concert aria “Ch’io mi scordi di te” by Mozart. The concert aria genre basically died with the 18th century, but in its heyday it was a convenient way for composers to accommodate singers they were courting for their operatic events. Each aria is a stand-alone, not associated with any theatrical production, but rather designed for the recital hall.

Mozart reworked the poem of this piece from an additional bit of material he composed for “Idomeneo.” It is a highly dramatic work that cries out for a big voice. On Wednesday, it received such a voice.

Coming off a successful appearance at the Metropolitan Opera in “The Marriage of Figaro,”Ms.Isokoski declaimed confidently and securely, if a bit unemotionally. I loved the sound, but was less invested in the believability of the character. This particular concert aria had an unusual adjunct: the piano obbligato performed by Mitsuko Uchida.

Ms. Uchida stayed onstage for a runthrough of Mozart’s Piano Concerto K. 537, known as the “Coronation.” She seems to have lost a step these past few years: This realization was less accurate than I would have hoped for, and not especially crisp. There was a pleasantly controlled relaxation to Ms. Uchida’s playing, but no real fire or gravitas. Mr. Davis had the orchestra sounding splendid, however – this big, full ensemble tutti was light years away from the wimpy period sonority favored by so many contemporary bands.

Ms. Uchida is now devoting much of her time to working with young people, especially as co-president of the Marlboro Music Festival in Vermont. She has correspondingly adopted the personality of the schoolmarm, admonishing the crowd with her finger to her lips to pipe down so that she could start the Larghetto. Her warnings went largely unheeded, and she had to abort her commencement of this otherwise lovely movement. Just outside, the illusionist David Blaine is attempting to stay submerged in water for a week; these people can’t keep from coughing for 20 minutes.

After intermission, Sir Colin shifted gears dramatically with two works by Jean Sibelius.The first, “Luonnotar,” is a real rarity: Even Ms.Isokoski, a homegrown Finnish singer, needed to have the music in front of her.

The flowering of an idea the composer nurtured for more than 20 years, this is a paean to nature in the form of a song for soprano and orchestra. It also explores the musical connection between Finland and the Western provinces of China, the vestige of which can be heard in the Finnish language itself. Mr. Davis painted with a delicate brush, appropriate for a composer who, as a child, saw different colors when his mother played chords on the piano. Ms. Isokoski was suitably soaring and lyrical, taking flight like one of the wild birds of the text from the “Kalevala.”

“Luonnotar” had previously been performed by the Philharmonic only once, with Phyllis Curtin as the soloist. This is not surprising, but the fact that those same 1965 concerts, with Leonard Bernstein conducting, included the last performances of Sibelius’s Symphony No. 3 is shocking. Forty seasons without playing such a major masterwork is about 39 too many.

Bernstein was a masterful interpreter of the Sibelius symphonies. Sir Colin matched him stroke for stroke this evening, eliciting a superb performance from his charges. The outer movements were thrilling in that pantheistic, song of the forests sort of way, but the crown jewel of this rendition was the middle Andantino.

The movement contains one of the most beautiful melodies of the 20th century, a magical, self-regenerating tune that refuses to die away, constantly changing ever so slightly and memorably. Except for a brief, Beethovenian middle section of storm clouds, this main theme remains present throughout the work, gently but hauntingly insistent.

The Philharmonic had the measure of this lyricism expertly, sustaining the elongated horizontal line without any sense of raveling or complacency. This was truly impressive music-making. I can only speculate about how good this ensemble might have been had Mr. Davis been named music director some years ago.

The Philharmonic will repeat this program on May 5 & 6 at Avery Fisher Hall (Lincoln Center, 212-875-5656).