After seven games of the Premier League campaign, Everton had conceded a league-high 16 goals, including half a dozen in a 6-3 home defeat to Chelsea.
However, a 3-0 win over Aston Villa was backed up by Thursday's 0-0 draw at Lille in the UEFA Europa League, and Martinez is delighted that his players are showing signs of greater defensive stability.
"It's a team effort," he said in a media conference on Friday, ahead of Everton's trip to Burnley on Sunday.
"We work really well, we've been very solid and that probably ends up being reflected in keeping two clean sheets back-to-back.
"The whole back four and the whole team had good concentration [against Lille], which is important in any team."
Martinez responded to questions about criticism of his defence in his customary unflustered manner, explaining that negative comments are part of the modern game.
"You don't need to take players out of the firing line, if you want to be a professional football player you have to cope with that," he added.
"Criticism shouldn't affect any player's performance, it should be the opposite and it should be the challenge to use that in a good way.
"The team is getting stronger and sharper and the reflection in the scorelines has been there. We are a stronger team now than at the beginning of the season and I'm really excited about the potential of this squad for the months ahead."
Thursday's game against Lille was marred by pre-game clashes between supporters in France, and Everton released a club statement regarding the incidents on Friday.
"All available reports suggest that the first incident, on the night before the game, was an unprovoked and planned attack by local youths," it read.
"The second incident, early in the afternoon on matchday, in the city's main square, quickly escalated into unwelcome and unpleasant scenes.
"Events then, equally quickly, returned back to normal with well-mannered and good-natured celebrations that were evident throughout the club's stay in Lille. The club will now work with all authorities to find out what happened and why."
