Nadal came into the match underdone after back, appendicitis and wrist problems - and stomach troubles only compounded his struggles. The 28-year-old started well enough but uncharacteristic errors soon piled up as the third seed struggled.
In the third set, Nadal called for the trainer and complained of dizziness. He was bent over following rallies and pointed to his stomach, shaking his head at his entourage.
But Nadal showed grit to battle on against Smyczek, whose previous biggest win came against then world No.19 Jurgen Melzer back in 2012. The 27-year-old American played beyond his ranking, sending down 64 winners to Nadal's 43.
The pair went toe to toe in the final set before Nadal broke his opponent to lead 6-5 before claiming the win on his fourth match point. The Spaniard, who was runner-up last year, described it as a "tough night".
"I felt very tired after the first set," he said. "I had cramps around the body. I'm not in perfect shape.
"When I was serving for the third, almost throw up. So it was a terrible feeling."
Nadal's hard-earned win thrust him into a third-round clash on Friday with Israel's Dudi Sela. The world No.3 was unsure what condition he would be for the match.
"I suffered too much on court for three hours and a half," Nadal said. "I was suffering a lot. Too much. You know, it was not funny today the way that the match was.
"Obviously it is a very positive thing that finally have the chance to win, but, yeah, I hope to recover myself."
-AAP
