Seeking to become the first English winner of the Open since Sir Nick Faldo in 1992, Willett birdied four of his last eight holes to card an opening three-under-par 67.
“Playing for the first time pain-free was delightful,” said Willett. “The hernia healed up all right but they go in in three places and tore my obliques with one and that’s really been hurting.
“It was joyous sneezing without it hurting for the first time on Saturday. That sounds stupid but that’s where I’ve been. It was a good job we caught it so soon. I saw the doctor on the Sunday of Memorial. If we had left it, who knows?
“And who knows what else 2021 will bring? It might finish well. I hope so.”
Willett has slipped to 115th in the world rankings and is outside the automatic qualifying places for the Ryder Cup, but was invited to a dinner for potential team members by European captain Padraig Harrington during last week’s Scottish Open.
“I’m still hanging around because of winning at Wentworth (2019 BMW PGA Championship) but I’ve never had a good enough run to progress,” added Willett, who was out of form and failed to win a point on his debut at Hazeltine in 2016.
“Covid came along and I had to drop out of the Players (Championship), which dropped me out of the top 64 for the match play, which knocked me out of the top 50 for other things.
“I haven’t done that much wrong but things haven’t gone in my favour. As long as I’m fit and healthy and can still swing a golf club, anything can happen.
“There are big points up for grabs from here on in and I’ve obviously played before. If by some unforeseen miracle something does happen for me, I’ll be familiar with the guys who will be in the team.
“It was a nice gesture (by Padraig) and it was nice to see all the guys again.
“When he started telling stories I did get some tingles again. It is definitely something I want to do but I do feel it has been left just a little bit late this time.”