The Latics have started the Premier League campaign with 4-0 and 6-0 home defeats to Blackpool and Chelsea respectively, following on from an 8-0 hammering at the hands of Carlo Ancelotti's team on the final day of last season.
They kept a clean sheet in midweek - albeit at League One side Hartlepool in the Carling Cup - but now face a return to Tottenham, where they were crushed 9-1 last season.
Martinez refuses to compromise on playing positive football but insists his men must wise up at the back.
"I never go for a damage-limitation result, I always want to win and sometimes you are more exposed in that way," he said.
"We are very naive and we are still not ready in that department, and it is something we need to sort out very quickly. We need to be a bit different off the ball, a bit more ruthless and a bit more focused.
"You cannot concede cheap goals in the manner that we are doing at the moment.
"We are not far away from becoming a very good side but that has to come with hard work on the training ground and with commitment and focus. We have got that in abundance so I am excited, I am really looking forward to the challenge."
Shipping nine goals at White Hart Lane last time around could have been the cue for Wigan to sink without trace, but they immediately responded by beating Sunderland in their next game and did enough to finish six points clear of the relegation zone.
Martinez said: "The best test you can find in the Premier League is going to White Hart Lane. Last season was a hurtful scoreline, many people will remember that, but I am extremely proud of the way we reacted."
The Spaniard also defended under-fire goalkeeper Chris Kirkland, who has been the last line in a defence which has conceded 10 in two Premier League matches.
"Chris is a true professional, he has got great pride in his job and he is hurting at the moment," Martinez said.
"Now is the time to change the dynamics of the last results, the players don't deserve to be in the situation they are in now.
"He is experienced enough to deal with any situation, it is the moment to face adversity."
Steven Caldwell should be available to make his league debut at Spurs, with his brother and club captain Gary still sidelined after hip surgery.
England Under-21 midfielder Victor Moses will be sidelined for two to three weeks after damaging ankle ligaments in the win over Hartlepool, having only just recovered from a calf problem.