The Juilliard Baroque, a 10-member period-instrument assemblage recently formed by British violinist Monica Huggett, made its area debut Saturday at the Library of Congress in an all-Bach program that started weak and ended strong.

The second half offered vibrant performances of the Overture No. 2 (here in a reconstructed original version for oboe and strings) and the Fifth Brandenburg Concerto. In the latter, harpsichordist Kenneth Weiss navigated the huge cadenza with clean fingerwork and dramatic pacing. His ornamentation and agogic freedom in the slow movement were exemplary, as well, although it raised a question: Why was such playing so rare everywhere else on the program throughout the ensemble?

The most impressive performance of the evening was from oboist Gonzalo Ruiz, who handled the marathon difficulties of the overture with something approaching relish, even though his balky instrument protested at times. Perhaps it was just greater familiarity with the repertoire, but the tutti ensemble in both works was also noticeably more precise, and more purposeful in inflection, than in the first half.

Period-instrument groups get no special cachet from me; historical scholarship does not give anyone a leg up on musical artistry. But the Juilliard Baroque showed, in these two pieces at least, that even the most overplayed repertoire can sound fresh and new when fine musicians pull together in a unified vision.

In the first half, a group of selections from “A Musical Offering” sounded slapdash; the aural novelty of hearing the plangent early woodwinds was not enough to compensate for the generic sameness of the playing. In the final “Ricercar a 6,” and even more so in the opening work (a concerto in A minor for the same forces as the Brandenburg), the conductorless ensemble lapsed into a tedious plod, with the players’ individual, random inflections amounting to a generic soup.

A mixed bag, then, but a skilled, sturdy group. I hope we hear more from them.

Robert Battey