The Portugal winger, on loan from Manchester United, controlled a throw in with his head and then unleashed a vicious, dipping shot which flew into the top corner, midway through the second-half.
The 28-year-old was overcome with emotion, clearly weeping as he was mobbed by his team mates
"It was a goal like any other," he told reporters. "I received the ball, saw the goal, shot and I was lucky."
"I thought about myself and everything that I have gone through," added Nani, who was born in Cape Verde and had a tough upbringing in Lisbon after his family emigrated to Portugal. "It's personal stuff, that nobody knows about."
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Junya Tanaka had opened Sporting's account when he bundled the ball home with his thigh following a corner early in the second half.
Sporting are third in the table with 47 points, nine behind Benfica who beat Moreirense 3-1 away on Saturday. Second-placed Porto (49) face Boavista on Monday.
(Reporting by Brian Homewood; Editing by Greg Stutchbury)
