According to the return match clause, after the war of antipodes of 1960 between Botvinnik and Tal, negotiations about the new match began.

Already toward the end of the 1960 match, Botvinnik started thinking about the potential return match. According to Garry Kasparov (On My Great Predecessors, Part Two, Page 231), Mikhail Moiseevich told him he asked Goldberg at a meeting of his helpers: What do you think, Grisha, should I play the return match?

Blinded by Tal’s brilliant play, his seconds weren’t convinced it is such a good idea. Botvinnik, being the stubborn and consistent man he was, „[…] realized that the return match definitely had to be played.!“ Almost immediately after the return match, he started seriously preparing for the upcoming clash.

Tal, on the other hand, was far from his best form. Already back then, his lifestyle started taking its toll. Being a heavy smoker and a drinker, he fell seriously ill just before the match. Riga doctors advised him to defer the start of the match by a month. USSR Sports Committee was ready to agree, but Botvinnik demanded (!) that Tal should come to Moscow for an official medical examination. Upon hearing this, Tal apparently said: „Never mind, I’ll beat him as it is!“.

Unfortunately for fans of the Riga magician, the course of the match proved that such an attitude was way too optimistic. The return match was supposed to be the second battle of antipodes, but it was no battle – it was a one-sided slaughter.

The match was held in Moscow between March 23rd and May 20th. Already the first game indicated Tal’s future problems with the Black pieces. And indeed, after the first 15 games, Botvinnik was already in a commanding lead – 10-55. In his first eight Black games, Tal only drew once and lost staggering seven times. At that point, the match was virtually over. Tal retained some hope with the wins in the 17th and 19th games, but Botvinnik retaliated in the 18th and the 21st games and won the match ahead of schedule with the convincing 13-8 score.

Thus, Botvinnik once again won the title of the World Champion. Although many attributed his victory to Tal’s condition, Mikhail Nekhmenevich himself admitted Botvinnik’s victory was well deserved:

“I think that I lost to him because he beat me! He was very well-prepared for the second match. Botvinnik knew my play better than I knew his.”

Sources:

Garry Kasparov On My Great Predecessors, Part Two

Chessgames: Botvinnik – Tal, 1961