Not Friday's season opener: Even obscure moments were arresting in a program titled "Orchestral Music from Hamburg." The evening at St. Mark's Church illuminated a wellspring so frequently utilized by more towering figures of the period, the concert might have been called "Handel: The Air He Breathed and the Music He Pilfered."

The program notes stated Handel stole much music from Reinhard Keiser (1674-1739), who directed Hamburg's opera orchestra when Handel was a young member. Though no particular Handel-recycled melodies came to mind in Keiser's Concerto in D (one of the works having its modern premiere), much of it and the rest of the program had such a sense of Handelian cross-pollination, you felt as if you were discovering lost cousins.

Though Italian concertos have such rhythmic regularity as to be called sewing machine music, this music could be flagrantly interruptive. Bold slashes of sound came out of Keiser's concerto. Other passages were full of such unanticipated events that the music seemed to fall down a rabbit hole - a reminder that for every solid, uneventful Johann Friederich Fasch (whose revival by a number of baroque specialists is something I have yet to appreciate) there's a C.P.E. Bach, whose Hamburg Symphony No. 4 broke off movements in midsentence.

The so-called overtures and concertos weren't in anything resembling the codified format of later decades, but were suites with nonstandardized numbers of movements that often seemed like operas without words, particularly Overture No. 6 by one Philipp Heinrich Erlebach. Even when operatic, the music seemed to double as a concerto while displaying sections of the orchestra purposefully and taking on a relatively symphonic manner. For all its surface formality, this corner of the baroque repertoire is so freewheeling that titles were irrelevant.

Even the music of Georg Philipp Telemann, which can give new meaning to autopilot, was fully awake in the Concerto in F, and gave Tempesta concertmaster Emlyn Ngai an extended, seven-movement workout that revealed previously detected but not necessarily heard virtuoso chops. On other fronts, the orchestra (impressively expanded to 22 players) often played with operatic passion, sometimes at the cost of stability. But even mishaps, which happen when valveless horns are part of the orchestration, gave the music an exciting brinksmanship.