Roger Federer came through his return to laugh at Richard Gasquet with a comfortable 6-2 6-3 victory and is now facing Monfils in 16 rounds.
Federer is in Novak Djokovic's side of the draw and would meet him if both reach the semifinals in Madrid.
But first, the match with Monfils is on the agenda, and the Frenchman is looking forward to it.
"I am slowly approaching the fight against Roger and hope for a little less wind and better conditions," he said.
"It's fast and he likes these conditions. He's more comfortable (and) I need a more aggressive tactic.
"There won't be millions of collections."
Federer is looking for his 1200 ATP Tour single-match victory and spoke after Gasquet's victory said: "I'm very happy to be back on clay.
"Super happy to be back here in Madrid. The crowds and the ovation I got before and after the match was fantastic. It makes you feel it was the right choice to come to Madrid so it felt good.
"The first game went well. I didn't think Richard was the best, far away. But from my side it was a good game."
Roger Federer vs Gael Monfil's live stream – how to watch
Roger Federer's fight against Gael Monfils is being streamed live on Amazon Prime Video.
This year, Prime Video sends live study coverage across tournaments, among others. at BNP Paribas Open from Indian Wells, Feber Tree Championships from The Queens Club, US Open and Nitto ATP Finals from The O2.
On-site field reporters will bring customers the latest actions, analyzes and comments right from court to many tournaments.
In addition to 37 ATP Tour events and the US Open, available exclusively on Prime Video with Prime membership, Prime members in the UK who subscribe to Eurosport Player via Prime Video Channels for an additional £ 6.99 per Month (after a 7-day free trial) will also benefit from the full coverage of the French opening and daily highlights and live coverage of the men's and women's finals at Wimbledon in 2019.