The Colombia forward has been struggling to live up to his $40 million price tag since joining Atletico from Porto in July and the 29-year-old's goal against the Kazakhstan champions was only his second of the campaign in all competitions.
Martinez was brought in as a replacement for Croatia forward Mario Mandzukic, who was sold to Juventus, but has yet to reproduce his form from the Portuguese league where he was top scorer in each of his three seasons with Porto.
"It was like a release because of what had been happening in previous games," Martinez told Spanish television. "I was calm even though the goal wasn't coming. Now I want to keep going the same way."
Martinez should get another chance to add to his tally in Atletico's next outing, a La Liga clash at home to fellow Champions League participants Valencia on Sunday.
Atletico coach Diego Simeone has been keen to protect his expensive new recruit from criticism and said the reaction of the other players to his goal showed Martinez had their backing.
"The position of forward is different to the others," Simeone told a news conference. "You can see how pleased the team were from the television pictures.
"This makes us very happy because it demonstrates the group's support for the player which will without doubt give him confidence and security in himself."
Atletico's victory at the Calderon put the 2014 runners-up level on six points at the top of the group with Benfica, who were beaten 2-1 at Galatasaray.
The Turkish club have four points in third, with Astana on one point in fourth and last place.
Atletico travel to play Astana on Nov. 3, when Benfica host Galatasaray.
(Writing by Iain Rogers, editing by Peter Rutherford)
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