The Ligue 1 champions got their Champions League campaign off to a promising start with a convincing win at the Karaiskakis Stadium.
And it was their threat from dead-ball situations that really stood out, with Motta nodding home two Ezequiel Lavezzi corners after the interval.
"It is not a coincidence that the set-pieces worked well, because we've been working hard on them in training," the Italy international told beIN Sport.
"But normally I am not in a scoring position as I'm the one taking them. This time around it worked, while in the last games it did not work with me. Tonight I got lucky."
Despite his own excellent display, the 31-year-old was keen to focus on the overall performance of Laurent Blanc's team, for whom Edinson Cavani and Marquinhos also scored.
"The most important thing was to win the game," he added. "We were missing something in the first period, but we recovered well."