Speaking to the club's official website, Martinez said: "We have to remember that Sunderland came well organised. They had a solid structure behind the ball.
"But I thought the second half performance was terrific. We put Vitor Mannone's goal under a lot of pressure. We didn't get any points but performances like that will get us positive results over the course of the season.
"The players showed an incredible attitude and tactical understanding to cope with the numerical disadvantage. We created numerous chances and had 11 corners, but the only critical aspect is that we need to score goals when we get those sort of situations."
The loss leaves the Blues in fifth in the Premier League table.