London - Alexander Zverev revealed a stomach bug left him on the verge of quitting before the world number three battled back to beat American youngster Taylor Fritz 6-4, 5-7, 6-7 (0/7), 6-1, 6-2 at Wimbledon on Friday.
Struggling with an illness that left him vomiting during a break in play, Zverev had just lost the third set when bad light forced play to be suspended late on Thursday evening.
The 21-year-old German didn't feel much better when he returned to court on Friday morning and considering pulling out during the on-court warm-up.
"I had a stomach virus. Yesterday I had pain during the whole three sets. After the second set, I actually went to throw up during the toilet break," he said.
"Today in the warmup I was actually maybe thinking about it, not to play at all. I was very low energy. I didn't eat anything since yesterday.
"But then I thought, Well, if I don't feel well, it's going to be one set. If I feel better, it might be two. Thought I'd go out there and try."
Zverev's gamble paid off, but he was left confused when asked if he revelled in such a masochistic display.
"I don't know what a masochist is. I won 6-1, 6-2 fourth and fifth. It was very easy," he said with a bemused expression after his Court One victory.
"I know that Wimbledon is used to be played after 9pm. For me, because it's such a closed court, for me the court is dark at 7.30pm.
"For me, we played in darkness for one and a half hours. That's why I couldn't really see his serve.
"Today I was returning much better, as I said, because it was brighter."
Zverev has plenty of practice at scrambling out of trouble after three times winning from two sets to one down at the recent French Open.
He staged another impressive escape act against Fritz and insisted he didn't care how he got the job done.
"What can I do? I'm down two sets to one every single time when I play five sets," he said.
"I'd rather go five than lose in four, be out of here, book a flight for me to go home tomorrow.
"I'm in the tournament. I'm playing third round tomorrow. That's what matters for me."
Zverev will face Latvian qualifier Ernests Gulbis for a place in the last 16.
After enjoying the best Grand Slam run of his career when he made the French Open quarter-finals last month, Zverev is hoping to reach the last eight at Wimbledon for the first time.
He was beaten in the fourth round last year.
Following early exits for Swiss 16th seed Borna Coric and Canadian world number 25 Denis Shapovalov, Zverev's win was a boost for the group of young prodigies branded the sport's 'NextGen' stars by the ATP.
Claiming he is starting to fulfil his vast potential, Zverev added: "The difference between now and a year ago, probably a little longer ago, is that when I'm down two sets to one or something like that, I don't really panic.
"I'm very calm. I try to find ways to win. I think that's a very big difference."
Wimbledon results on Friday, the fifth day of the 2018 championships (x denotes seeded player):
Alexander Zverev (GER x4) bt Taylor Fritz (USA) 6-4, 5-7, 6-7 (0/7), 6-1, 6-2
Gael Monfils (FRA) bt Sam Querrey (USA x11) 5-7, 6-4, 6-4, 6-2
Kevin Anderson (RSA x8) bt Philipp Kohlschreiber (GER x25) 6-3, 7-5, 7-5
Donna Vekic (CRO) bt Yanina Wickmayer (BEL) 7-6 (7/2), 6-1
Evgeniya Rodina (RUS) bt Madison Keys (USA x10) 7-5, 5-7, 6-4
Camila Giorgi (ITA) bt Katerina Siniakov (CZE) 3-6, 7-6 (8/6), 6-2
Ekaterina Makarova (RUS) bt Lucie Safarova (CZE) 4-6, 6-4, 6-1