The Edinburgh Festival Chorus has been every director of the International Festival’s secret weapon for over half a century – the event’s great local asset, enhancing performances and boosting box office.

So the Philadelphia Orchestra’s insistence on Covid protocols that has prevented them singing Beethoven’s Ninth Symphony in the last week of the Festival is a bit of an insult, but one that should be seen in the context of a busy 75th Festival for the choir, from Carl Orff’s Carmina Burana at the start to Elgar’s The Dream of Gerontius at its end.

The singers were on song on Saturday too, especially the women’s voices, for Janacek’s Glagolitic Mass, a demanding work from the early part of last century that requires them to sing in an Old Slavonic tongue that is foreign even to people who live in the Czech Republic.

But this concert was not really about them as much as the return of the Czech Phil, making its first Festival appearance with current Chief Conductor and Music Director Semyon Bychkov, having been scheduled to appear at the 2020 Festival.

The first of its two concerts began with Dvorak’s Carnival Overture, the conductor’s precise beat urging the strings on from the start, the eight double basses making a superb contribution alongside the bass trombone and tuba, on what was a grand night for fans of crisp brass playing.

Martinu’s Concerto for Two Pianos, composed by the Czech émigré for the Philadelphia Orchestra during the Second World War and the soloists on Saturday, Marielle and Katia Labeque, also have an astonishing history with the Edinburgh Festival, dating back almost 40 years.

The French sisters are masters of the work’s percussive complexities, and the composer’s melodic style surely hugely influential on Leonard Bernstein.

The orchestra’s wind section had a generous share of the spotlight in the slow movement, alongside principal viola Eva Krestova.

With a quartet of mainly Czech vocal soloists led by Russian soprano Evelina Dobraceva and Daniela Valtova Kosinova at the Usher Hall organ, Janacek’s Glagolitic Mass had forces of the ethnic authenticity the composer would have wanted, with tenor Ales Briscein and the orchestra’s timpanist also much to the fore.

A work that is sometimes seen as an oddity was more a full-throated 20th century updating of an ancient form in this performance, its lack of contemporary competition perhaps an indication of a decline in religious observance, and its music Janacek at his original best.