The 19-year-old Liverpool winger, who is spending the season on loan at Sheffield Wednesday, provided the assist for Isaac Price’s second goal as Northern Ireland moved to seven points from three Group B2 matches.
Morrison was one of three changes made by O’Neill in Trnava after remaining an unused substitute for the opening games against Georgia and Hungary.
Playing as an inside forward on the right, he made an immediate impression and felt he had repaid the manager’s faith after waiting for his opportunity.
“I've been biding my time after the first two games,” Morrison told BBC Sport.
“I was training well, working hard and I'm glad he [O'Neill] trusts me enough to give me the start. I think I did well enough.”
His delivery created the second goal when he crossed for Price to head home his 11th international goal, giving Morrison another reason to believe he can retain his place against Georgia at Windsor Park on Monday.
Price was quick to praise his international team-mate after the victory.
“Thought he was really good,” Price said. “He's a different threat than what we have had before. A really good crosser of the ball and he has come in and given the manager a headache with a game on Monday.”
Morrison admitted, however, that delivering the cross was not initially his intention.
“To be fair I wasn't going to cross it,” he said. “I was like 'OK, get the ball and do some stepovers', but it was just set it back to me and I whipped it in and Isaac was there.
“Every time I got the ball, I was just trying to make something happen.”
Morrison represented England at youth level but qualifies for Northern Ireland through his Newry-born mother. He made two senior appearances for Liverpool last season and is now hoping to make his first appearance at Windsor Park.
“It's going to be great,” he said. “I've never played at Windsor Park. Hopefully I get the start, if I don't get the start, hopefully I come on and impact it.”
With Northern Ireland unbeaten across their opening three matches, Morrison’s performance has given O’Neill another option in the attacking positions ahead of Monday’s meeting with Georgia.