Eight-time champion Roger Federer avoided a huge Wimbledon upset as injury robbed France's Adrian Mannarino of the chance to earn a memorable win.
Sixth seed Federer, 39, trailed 6-4 6-7 (3-7) 3-6 4-2 when Mannarino slipped and injured his knee.
The world number 41 battled on and lost the fourth set, then retired after one point in the decider.
A sympathetic Centre Court crowd gave a heartfelt ovation as Mannarino, on his 33rd birthday, limped off court.
"It is awful, it shows that one shot can change the outcome of a match, a season, a career. I wish him all the best," said Federer.
"I hope he recovers quickly and we see him back on the courts. He could have won the match."
The Swiss 20-time Grand Slam champion will play France's Richard Gasquet or Japan's Yuichi Sugita in the second round.
Meanwhile British number one Dan Evans reached the second round of Wimbledon with a straight-set win over Feliciano Lopez.
The 31-year-old will next face either Dusan Lajovic of Serbia or Frenchman Gilles Simon.
"It was great. It's amazing to be back playing at Wimbledon again. I didn't realise it was going to be as busy," Evans said.
"I'm delighted to win. I played some good tennis.
"The first set I was probably a bit too into myself, once I let go a bit I really got rolling.
"It was a good mental effort."
Elsewhere World number six Alexander Zverev prevailed in straight sets in his opening match against the Netherlands' Tallon Griekspoor at Wimbledon.
US Open finalist Zverev reached the French Open semi-final earlier in June.
Australian 15th seed Alex de Minaur was stunned by 20-year-old American Sebastian Korda in four sets, the world number 50 triumphing 6-3 6-4 6-7 (5-7) 7-6 (7-5).
And Argentine ninth seed Diego Schwartzman defeated an uninterested Benoit Paire 6-3 6-4 6-0.
The Frenchman was given a warning for unsporting conduct for not trying towards the end of the third set, and received whistles and jeers from the crowd for walking off and taking a seat in response.