The 36-year-old only need a semi-final finish at last week's Rotterdam Open to replace the Spaniard at the summit of the ATP standings, but went on to scoop his second title of 2018 with victory over Grigor Dimitrov.
Nadal has not played since withdrawing in the fifth set of the Australian Open quarter-final against Marin Cilic with a hip problem and is not due to be back in action until next week's Mexican Open.
Having seen Federer prevail, Nadal – who has 300 ranking points to defend after finishing as the runner-up in 2017 - is unable to return to world number one in Acapulco even if he wins the event.
But the tournament kick-starts a key period of the season which includes the Sunshine Double – the BNP Paribas Masters in Indian Wells and the Miami Open – which is followed by the clay court campaign.
And Nadal is fully focused on performing to his best during this sector of 2018 and will not allow himself to be distracted by the top of the rankings.
"He didn't need to return to number one to show who he is in tennis. What he's achieved is very difficult and you can only congratulate him.
"Rankings don't lie, he did a little bit better than me in the last 12 months," he told the media in Mexico, according to Tennis World USA. "I've been in the top two for many years. Being number one, three or five doesn't make much difference.
"What makes me happy is feeling competitive and able to win tournaments. I won't fight to be back at number one. I'll fight to have my best possible season. If that means later in the season I have a chance to be back at it, OK. I only fight to be happy and competitive in every tournament I play. That's my goal. We'll see where I'm at the end of season.
"I started the season at a good level. The injury in Australia was an accident. I'm heading to the swing of Acapulco, Indian Wells and Miami with a high motivation and then comes the clay. The period from Acapulco to Roland Garros is a very important part of the season for me."