The Argentine was unhappy with his side after they were beaten for the first time this season on Tuesday
The home side were 2-0 up before half-time thanks to goals from Thulani Serero and Danny Hoesen and though Xavi pulled one back for the Blaugrana with a 49th minute penalty, the hosts held on for all three points despite being reduced to 10 men following Joel Veltman's dismissal.
Martino told reporters after the game: "We lacked intensity to play the game, Ajax came out very strong in the first half. In the second half the game was something else and more like a typical Barcelona match.
"We have to reflect a little together, to learn why we played with a different intensity. It is true that we have a secure classification and Ajax had to try to win the game, but we cannot afford to play the first part like today."
The 51-year-old was also quick to express his disappointment with the lack of cutting edge shown by his side following their inability to convert their usual dominance of possession into meaningful opportunities in the final third.
"We have to do more in possession of the ball," he continued. "There were times when the opponent played one-on-one and we had no problems there.
"But we lacked mobility at times and accuracy with the ball - what we have to change is firmly not to repeat our first-half performance."
Carles Puyol operated in an unfamiliar right-back role on Tuesday night, but Martino was quick to defend his decision not to play the 35-year-old in his usualy centre-back slot.
He added: "We were missing some players defensively and I felt that we needed more depth at the back and so he started at right-back."
Barcelona remain top of Group H on 10 points, while third-placed Ajax trail AC Milan by just a point ahead of the final round of group stage fixtures, as the race for second place goes down to the final matchday.