The fact that Yesterday was one of those songs should come as no surprise, especially considering that there had been much discussion about issuing it as a single in England by the Beatles, their producer George Martin and manager Brian Epstein back in June when it was recorded. The merits of the tune were obvious but, since Paul was the only Beatle performing on it, it was problematic. Ultimately, it was decided that the record was not representative of the Beatles as a group, nor should it be released as a solo piece credited to Paul McCartney.
Capitol was not bound by such artistic constraints and, as the song was already gaining considerable attention despite being buried as the thirteenth track on the current British album, the label was free to issue it as a single attributed to the Beatles in the US market. The surprise here is that it was not originally supposed to be the A-side.
That's right. Ringo's popularity among American fans was still so strong that his country and western cover song Act Naturally was initially chosen to be the A-side of the single. Fortunately, the powers that be at Capitol came to their senses in time and flipped the two songs before the single was issued. According to Wikipedia, this decision was made so late that Capitol never corrected it in the company files. I can confirm that the Capitol version of both the Red and Blue Albums in 1973 contained a cardboard insert listing all albums and singles issued on the label to date, and this single was still listed at that time as Act Naturally/Yesterday.
Released on September 13th, the record became the second Capitol-created Beatles' single (after Eight Days a Week earlier in the year) to hit the number one spot.