Steven Isserlis and Robert Levin at 92nd Street Y When last encountered, in March, the cellist Steven Isserlis was doubling as instructor and performer at the Piatigorsky International Cello Festival in Los Angeles, dispensing wisdom in a master class one day and shining in works by Fauré and Thomas Adès in the closing concert the next. Last week Mr. Isserlis functioned in a similar dual capacity at the 92nd Street Y in partnership with the fortepianist Robert Levin. After a lecture-recital preview on Wednesday evening, Mr. Isserlis and Mr. Levin performed all of Beethoven's works for cello and piano on Thursday and Saturday evenings. Steven Isserlis, who performed with Robert Levin on Thursday night at the 92nd Street Y. In an article reprinted in the program book Mr. Isserlis wrote that like many another "sniveling musician," he had been slow to come to Beethoven, having indulged in "a pathetic little show of resistance." But he eventually began to perform one or another of the five sonatas for piano and cello (as Beethoven styled them), and by 2004 he had become enough of a zealot to tackle all the works for those instruments with Mr. Levin in Boston. The two repeated the survey in London in 2007 and again last month, and the Y performances were part of a sporadic tour leading up to recordings of the works. The Thursday recital, the only one I could catch, included two sets of variations (on Handel's "See the conqu'ring hero comes" from "Judas Maccabaeus," and Mozart's "Mädchen oder Weibchen" from "Die Zauberflöte"); a Sonata in F transcribed from the Horn Sonata (Op. 17); and two sonatas for piano and cello: the formative F major (Op. 5, No. 1) and the magisterial A major (Op. 69). Not surprising given their experience together and their continuing partnership, Mr. Isserlis and Mr. Levin proved kindred spirits, each matching the other's phrases in temperament and dynamics, right down to the quietest turn of phrase. But what was most impressive - and Beethovenian - was the power of their climaxes, especially in the A major. Even to a fan of early instruments who has never entirely warmed to the fortepiano, the balance between instruments here quickly came to feel just right. And that was especially true in loud outbursts, where the performers were able to match not only dynamic levels but also energy levels. It is one thing on a modern piano to choose a loud dynamic more or less arbitrarily to match the energy of the cello playing full out. It is something altogether different when the fortepiano also has to play full out to match the cello's output. These players, pushing each other to the limit, achieved a gripping excitement seldom heard in these works from the combination of cello and modern piano. As an encore they offered another transcription: this one of music written for - and wasted on, in Mr. Isserlis's words - the mandolin. What chance would that instrument have against the modern piano? Steven Isserlis and Robert Levin repeat the Beethoven recitals on Saturday and Sunday at the Herbst Theater in San Francisco; (415) 392-4400; sfperformances.org.