Portugal had plenty of the ball against the African side but produced seven shots and only one on target - Joao Neves's sixth-minute header.
Martinez said on Monday his players started that match brightly but lost discipline and structure after the first 20 minutes - something they would improve on against Uzbekistan.
"We are strong and focused," Martinez said. "And our group is even more united than before. It is a process. Tension is not part of our team.
"It’s normal to have criticism after a poor result. Sometimes it's unfair or negative, but it is not part of how we prepare."
All Portugal's players aside from Tomas Araujo are available for the match, including Ruben Dias, who sat out the opener, he added.
Martinez also defended Cristiano Ronaldo, whose performance against Congo prompted calls for the 41-year-old to start on the bench against Uzbekistan.
"We are a team that wants the ball," Martinez said. "We want to defend and react quickly. We want to counterattack quickly. You need a player that opens up space with movement and Cristiano is one of the best to do that.
"He is a player who has been defending and playing for his country for a long time and he wants to keep improving for the team. He is really a role model for the team."
With Colombia beating Uzbekistan 3-1 in their opening match to top Group K, Martinez said his team know a victory is important to keep pace with the South Americans and secure a place in the knockout phase.
"The feeling of disappointment is one we all have as a team," Martinez said. "Tomorrow I do feel like we will have a team that will be ready to perform for 90 minutes at the level we have."