It was only through a litany of roster changes that the Orchestra Mozart’s London debut at the Royal Festival Hall took place at all. Beginning with Claudio Abbado and Martha Argerich down to play Haydn and Mozart, a dual cancellation meant Bernard Haitink and Maria João Pires had to step in at what may as well have been the last minute. With them changed the programme, leaving us with an all-Beethoven concert contrasting the high drama of the second Leonore overture with the relatively unrestrained optimism of the Second Piano Concerto and the Fourth Symphony, both in B flat and with not a minor-key movement between them.

Most know only the third Leonore overture, but that piece’s huge dramatic scope only slightly overwhelms the sweep of the second. The rich, slow introduction showcased the near-impeccable ensemble of this orchestra; I don’t think I heard a ragged entry all night, and woodwind intonation was spot-on. The violins in particular must receive special praise; many is the performance where the dashing semiquavers before the triumphal song that closes the overture are, to put it mildly, slightly questionable. Throughout, however, the violin section playing in unison sounded for all the world like one player amplified. Leader Raphael Christ’s enthusiasm infected the whole orchestra, and one could see clearly the level of intercommunication taking place amongst the players on stage. It was in the absolutely magical transition to Leonore’s Allegro that it really became apparent we were hearing Abbado’s orchestra; from the quietest pianissimo to a gloriously balanced forte, this was a crescendo where every member of the orchestra was totally alert to their surroundings. Even on the grand scale of opera, this was chamber music; from gorgeous quiet woodwind chords to the fullest tutti, Orchestra Mozart simply does not seem to struggle with balance at all. Though Haitink is without doubt a traditionalist and this interpretation reflected that, his authority shone through the totally unified vision of the orchestral performance in the overture and throughout the concert.

Unfortunately Pires did not seem to share this vision, the styles (and, oddly, intonation) of orchestra and soloist often seeming quite at odds. Marred from the start by a rather over-bright, almost jangly instrument, Pires’ performance was quite lacking in tonal detail, the many lyrical episodes sounding surprisingly percussive and detached for a pianist with such an “aristocratic” reputation. An apparent dearth of substantive phrasing was married to a highly Classical conception of this, the earliest of Beethoven’s piano concertos (despite its place in the order of publication); never was the passing moment allowed to linger, tempos marched along uncaring how beautiful any given turn of harmony. This sounded suspiciously like Pires’ characteristically “highbrow” Mozart, but there is much in the second concerto that can only be Beethoven. It was only in the last movement that it felt like both parties were playing the same composer, but by then it was too late.

It was good to hear the orchestra restored to its full size in the symphony after having shrunk for the concerto. The woodwind, however, no longer seemed as clear and lustrous as they had before. Articulation seemed more sluggish, the sound less focused, and against a string section coming yet more into its own, the winds seemed rather characterless for much of this performance, despite still-impeccable intonation. But what strings! From sharp-edged syncopations in the first movement, to an almost Brahmsian warmth in the slow movement, to madcap semiquavers in the finale, the string section’s infinite adaptability stole the show.

Only in the finale did the orchestra again play with the breathtaking oneness we had heard before, highly controlled dynamics untroubled by the perpetual motion of Beethoven’s devilish writing, particularly impressive at Haitink’s brisk tempo. It was only in the slow movement, taken at a very flowing pace, that I would have liked to have heard some expressive to-and-fro of tempo, but the playing (particularly from solo clarinet Alessandro Carbonare) was sufficiently beautiful that it didn’t really matter. This was, again, a traditional Beethoven reading from Haitink, but, just as with Leonore, total expressive intensity and unity of message meant it was never allowed to become dull.

I must wonder, though, whether the overture to Egmont was really the best choice for an encore. Returning to the high, serious drama of the Leonore overture, Egmont’s character seemed rather out of sorts with the more-or-less untroubled gaiety and positivity of the two works we had heard since. Despite a blisteringly intense performance all round, I couldn’t help but feel like the change of pace was slightly inappropriate. The audience’s joyous response, on the other hand, suggested that I was worrying about nothing, and when I couldn’t help but smile at the brass players dominating the orchestra at Egmont’s close, I suspected they may have been right.