The Spaniard made a poor start to the match and lost his first serve, but he quickly hit back and won the next game, before making a decisive second break in the eighth game of the set after a long forehand from Wawrinka to go 5-3 ahead.
Nadal made no mistake in the next game to serve out the set and he quickly raced into a 4-1 lead in the next set, after breaking his Swiss opponent twice.
He then comfortably served out the rest of the match to seal a 6-2 win over the French Open champion, and ensure a winning start to his tournament.
"I'm very happy to be back, the last year has been tough," BBC Sport quotes Nadal as saying.
"Without any doubt, this is one of the best tournaments in the world, in a great city. I'm very happy to start like this, that's important for my confidence. The last couple of weeks I've been playing well. I have the same motivation, the same spirit to keep improving my tennis."
Nadal will return to action at the O2 on Wednesday evening with a clash against Andy Murray. body check tags ::