After playing so well in beating fellow strugglers Reading 3-0 last week, the last thing the Latics needed was to fall behind so early in the match, but were up against it after only two minutes.
"The first goal showed a real lack of concentration as Downing had a free header in the six-yard box," he said.
"The first 20 minutes we were very soft and defensively nowhere near where we needed to be.
"That (first) goal had a snowball effect on our performance."
Martinez denied not having a method of negating the threat of Luis Suarez, with the Uruguayan's hat-trick costing them dearly.
"If you look at the stats at the end we had as many shots on target as they had but the performance of Pepe Reina had a bigger effect on the result than us stopping Luis Suarez," he added.