Porto played out a 1-1 draw in Switzerland on Wednesday, having dominated the match.
And yet they could have come away with a defeat as Derlis Gonzalez's 11th-minute goal had seen the hosts lead until the latter stages of the contest.
But Danilo's 79th-minute penalty ensured Porto snared the all-important away goal after both Cristian Tello and Casemiro had earlier seen goals ruled out.
Martinez said: "This result puts in a good position.
"We accomplished part of our objective for this game, but there are still 90 minutes to be played.
"We will have to be focused when that match [second leg] arrives, but we will have plenty of time to think about it."
Goalscoring hero Danilo echoed the thoughts of Martinez and said: "It was a difficult game. We knew that the smallest mistake could be punished and that was exactly what happened.
"But we managed to level the score, which was important and we leave here with a good result. Now we have the home match to seal our qualification."
Porto host the second leg on March 10.
