Roger Federer admitted he got lucky after Adrian Mannarino was forced to retire from their first-round match at Wimbledon with a knee injury.
The Frenchman was two sets to one up and a break down in the fourth against a rusty Federer when he slipped and fell to the turf clutching his right knee.
Mannarino tried to continue but was severely hampered and, after losing the fourth set while barely able to serve, called it quits at 6-4 6-7 (3) 3-6 6-2.
Speaking on court, Federer said: "It's awful. It shows that one shot can change the outcome of a match, a season, a career. I wish him all the best and I hope he recovers soon. He could have won the match, he was the better player, so I got a bit lucky."
Conditions under the Centre Court roof do appear to be more slippery than when it is uncovered, and Serena Williams became the second casualty barely an hour, retiring in tears early in her clash with Aliaksandra Sasnovich after appearing to hurt her ankle.
Federer was in the press conference room when his fellow 39-year-old bade her farewell, and he admitted he took great care with his movement because of the conditions.
He said: "I do feel it feels a tad more slippery maybe under the roof. I don't know if it's just a gut feeling. You do have to move very, very carefully out there. If you push too hard in the wrong moments, you do go down.
"I do feel it's drier during the day. With the wind and all that stuff, it takes the moisture out of the grass.
"I feel for a lot of players it's super key to get through those first two rounds because the grass is more slippery, it is more soft. As the tournament progresses, usually it gets harder and easier to move on.
"This is obviously terrible that it's back-to-back matches and it hits Serena as well. Oh, my God, I can't believe it."
Mannarino, who described the grass as slippery and said he found it difficult to move, admitted he feared the worst immediately, saying: "I heard a big crack and knew straight away I wouldn't be able to do anything any more."
Federer had focused his recovery from two knee operations on being fit for possibly a final tilt at a ninth Wimbledon title and he was good enough in the first set against a player who plays his best tennis on grass and had made the fourth round here three times.
But the sixth seed, who turns 40 in just over a month, has only played a handful of matches in the last year and a half and suffered a dispiriting loss to Felix Auger-Aliassime at the warm-up event in Halle.
As the second set wore on, Federer began to make more and more errors, particularly off the forehand side. He played a poor tie-break and was then broken twice as Mannarino took a two sets to one lead.
Federer was staring at a first opening-round loss at a grand slam since before he won the first of his 20 titles 18 years ago, but he regrouped at the start of the fourth, saved a break point and began to play with more aggression.
Whether he would have completed the comeback became a moot point, with it immediately apparent that Mannarino's slip had done some real damage.
Federer, who will now face his old rival Richard Gasquet, said: "I tried to definitely mix up my game a little bit more again towards the fourth set because clearly it wasn't working in the third. He was getting too comfortable from the baseline, taking charge from there.
"I think I was maybe turning things around a little bit. I would have been interested to see if I got through that fourth set normally.
"It was just a terrible ending, one I don't like to see. I just felt really down, especially with everything I went through with my knee. I hope he's not out for a long time."
