Rafael Nadal confessed that he was close to withdrawing from his match against Tim Smyczek before rallying to produce a 6-2 3-6 6-7 (2-7) 6-3 7-5 win on Rod Laver Arena.
The 14-time grand slam champion required medical attention in the third set and, after falling 2-1 down, a shock second-round exit appeared to be on the cards.
But Nadal mustered all of his energy to overcome the American in absorbing fashion.
Afterwards, Nadal – who said he felt fine during the day – told reporters it could have ended so differently after enduring one of his toughest matches on court.
"I was close to not continue because I felt that I was very dizzy," the Spaniard said. "I felt very tired. I feel lucky to have the chance to finish the match.
"I tried to play much more aggressive, without running, no running anymore, and try to go for the winners and play little bit better, play little bit more relaxed."
Nadal added: "At the end of the first set, I start to feel my body very bad, very tired. I don't know. I was worrying crazy.
"Then when I was serving for the third, almost throw up.
"I suffered too much on court for three hours and a half. I was suffering a lot. Too much."