The two players returned this year from breaks in 2016 and have had career resurgences, winning a combined 12 titles and splitting the four Grand Slams between themselves.
While circumstances have allowed Nadal to regain the world number one ranking, a recurring theme this year has been Federer's dominance over the Spaniard despite boasting an inferior head-to-head record.
The Swiss ace most recently defeated Nadal in straight sets to win the Shanghai Masters in what was his fourth win over the 31-year-old following his victories in the Australian Open final, Indian Wells and the final of the Miami Open.
With 15 wins now compared to Nadal's 23, a big reason for Federer's recent success has been his more aggressive use of the backhand, according to Petchey.
"The Roger Federer backhand has been the big difference on return," Petchey said, as quoted on The Express.
"He's gone from chipping nearly 20% of them in the past against Rafa on hard courts to down at around 4% of chipped returns off the first serve and around zero on the second."
Petchey also believes Federer is mentally stronger, echoing what former French Open finalist Henri Leconte said about the 19-time Grand Slam champion, while adding that his denying Nadal break points has been crucial.
"His mind is clear," Petchey explained. "There's an absence of alternatives. He knows what he has to do and commits to it with conviction - and it's worked out."
"On break points against Rafa on this five match winning streak he's made 19 out of 25 serves on break points - that's such an advantage."
Federer, ranked two, is currently taking part in his hometown event in the Basel Open as he will face Benoit Paire in the round of 16 on Thursday (26 October).