The Argentine coach tasted defeat for the first time as Blaugrana boss as the Catalans slumped to a shock Champions League loss in Amsterdam.
Thulani Serero and Danny Hoesen put Frank de Boer's side two goals up before the break, only for Xavi to halve the deficit from the penalty spot early in the second half after Joel Veltman had been dismissed for a foul on Neymar.
However, the 10 men of Ajax held on for an invaluable win to keep alive their hopes of reaching the Champions League knockout phase, and hand Martino his first defeat since taking charge of Barca in July.
Prior the match, the Argentine coach had stressed he was not interested in the prospect of equalling Guardiola's 21-game unbeaten run, set back in the 2011-12 season, claiming he would rather emulate the Spaniard's trophy haul in 2009, when the Blaugrana finished the year with six titles.
Interestingly, Guardiola's 21-game unbeaten run - which came to an end thanks to a 1-0 defeat at Getafe - ended on Nov. 26, 2011 - exactly two years prior to Tuesday's defeat in Amsterdam.