Exactly 720 days had passed since Opera Philadelphia last performed for a live public — indoors — when the public filled 1,100 seats on Friday for a double bill of less-than-familiar works in concert performances at the Kimmel Center.

Listeners must’ve been hungry for it. Both the elegiac George Walker song cycle Lilacs (which won the 1996 Pulitzer Prize, a first for a Black composer) and Stravinsky’s opera-oratorio Oedipus Rex are more known about than heard, but were given full-tilt resources with an orchestra of 93 (far larger than what could fit in any local orchestra pit) under music director Corrado Rovaris.

It was very much a thinking person’s return to traditional performance: Lilacs deals with the death of Abraham Lincoln and Oedipus unfolds in the midst of plague.

This was not the feel-good evening of popular arias that Opera Philadelphia had last summer at the Mann Center with Lawrence Brownlee and Michael Spyres. Also, the more deeply examined performances that come with staged opera was not in the cards in this concert presentation . Both Walker and Stravinsky make singular musical demands that even the most resourceful performers can’t wrap their arms around with limited rehearsal time.

Walker’s Lilacs would seem to be straightforward with sensitive, adept vocal lines fashioned around Walt Whitman’s famous “When Lilacs Last in the Dooryard Bloom’d,” showing the composer distilling the wide range of musical influences that he worked with during his long creative life. But that doesn’t mean the fine points of his subtle word settings immediately reveal themselves. Soprano soloist Tiffany Townsend made lovely, heartfelt sound but hadn’t yet worked out optimum enunciation. Also, the orchestral writing is often a cloud of harmonic ambiguity and inconclusive endings that remind you how true grief has no closure. You got that from Rovaris, though that impression would’ve been stronger had the musicians a chance to live longer with the piece.

Was the choice to perform Oedipus — which begins with the city of Thebes besieged by plague — a coincidence? General director/president David Devan said he scheduled the work months back, anticipating that the pandemic would be nearly gone. As it turns out, the piece’s astringent opening felt like salt in wounds — though only momentarily.

The bigger problem is the 1927 piece itself. The composer scrupulously wanted to avoid any hint of vulgarity, and perhaps as a result, Stravinsky’s vocal writing is stilted and his Sophocles-based dramaturgy has an eccentric formality, with blocks of choral sound here and odd, wandering bassoon solos there. In Greek tradition, many plot points aren’t dramatized onstage so much as they’re related in narration. Luckily, Charlotte Blake Alston brought her fierce charismatic stamp to her own English-language version in the story of a king who realizes he killed his father and married his mother.

Though the larger-ensemble moments took on an epic sweep by the end, plenty of other passages were more about being musically correct than projecting the intention behind the notes. But if there’s one element that consistently gauged the piece’s emotional temperature, it was the timpani writing, as played by Martha Hitchins. Whether conveying racing heartbeat or distant thunder, Hitchins’ variation in sound and touch was an ongoing commentary as clear and eloquent in her own way as Alston’s.

In the Latin-language title role, tenor William Burden (a Philadelphia regular who is always great to hear) delivered a peak performance, finding pathos amid Stravinsky’s dramatic aloofness, but also delivering the kind of demanding rhetoric that remind you Oedipus was indeed a king. His wife, Jocasta, has more sympathetic music (it seems to come from a different opera) with lush-voiced Rehanna Thelwell making the most of it. Jonathan Lemalu was a beacon of dramatic confidence as Tiresius.

Was Stravinsky’s choral writing conceived to be sung with clinical clarity or dramatic momentum? Both would be ideal, but momentum was what Opera Philadelphia’s chorus knows how to deliver — and it did. Masks can be blamed for muddy textures, but in a strangely prescient footnote, masks are what the composer apparently wanted for some of the singers. Then again, composers don’t always know what’s best for them. And like the blinded Oedipus, Stravinsky often seemed to be groping in the dark on this piece. Let’s have some feel-good arias. Soon.