Martina, a summer signing from FC Twente, netted from 25 yards out with a sublime half-volley with the outside of his boot at St. Mary's.
It was the 26-year-old's first Premier League start and only his sixth appearance for the Saints.
"I don't have words - it was an unbelievable feeling," Martina told the club's official YouTube channel. "I saw the ball go in and I thought 'oh my God'.
"It was a great feeling, for sure. I shoot and after the goal everything was slow motion for me. I was so happy, so happy.
"I score I think three goals in my whole life and that's the nicest one.
"I'm very happy to have scored and I'm very happy that the coach gave me a chance.
"I need to improve to keep playing there and I'm very happy for the chance."