"It would be a snowball. It was not really about the ranking to be quite honest. If I was closer in the points race (to Nadal) it might have been."

On Sunday, Federer claimed his first success against del Potro in a Basel final, after the South American beat him in both 2012 and 2013.

He now has won a Tour-leading seven titles this season after beating Nadal in the Shanghai Masters final a fortnight ago.

Federer has also captured the Australian Open and Wimbledon titles in 2017.

He admitted frustration after failing to win the opening set on Sunday.

"Being up two breaks should be enough to beat almost anyone. I was also up in the breaker. I had way too many wasted opportunities," he explained.

"I didn't have the best serving day, I struggled. It was mental and physical, I'm glad I found a way somehow."

Del Potro will be playing for a fourth successive week in Paris after coming back earlier in the season from wrist problems, as he looks to snatch a late place for the eight-man event in London.

The 29-year-old reached the Shanghai semi-finals and won in Stockholm earlier this month before his run in Basel.

Federer lost only two sets during the week as he improved his head-to-head record to 17-6 over del Potro, with a third win in four matches against the former US Open champion in 2017.

"It's unbelievable how well Roger is playing," said del Potro. "I hope to be in such shape when I'm his age. But I doubt I will be."