The Swiss star won his 97th career title by cruising past Grigor Dimitrov in the Rotterdam Open final on Sunday.
After beating Robin Haase earlier in the tournament, Federer ensured that by Monday he will knock Nadal off top spot in the world rankings.
The 36-year-old is now the oldest player to ever be world No 1. And Federer’s Rotterdam title means he beats Nadal to another achievement.
The veteran is now the first man to win 20 ATP 500 World Tour titles.
Nadal trails his counterpart with 19 to his name.
But the duo are clear of tennis stars past and present.
Novak Djokovic and Pete Sampras have 12 ATP 500 wins.
David Ferrer has 10, while Boris Becker and Andy Murray each have six to their name.
But Nadal will be confident of overtaking Federer due to being five years younger than his foe.
And the Spaniard may end up achieving the feat if his persistent injuries remain at bay in the final years of his career.
Meanwhile, Federer has hinted he may soon call time on his playing days.
“I’m not sure how many more years I will be playing but I will never forget this week,” he said after his Rotterdam win on Sunday.