Another one was looming when Nadal was serving at 0-2 in the second set. He bent over at the waist to stretch his back and then grabbed his lower back with his hand and grimaced in pain. His serve immediately dipped to 141 kph (87 mph).
When Nadal took a medical timeout after falling behind a set and a break, and returned to a chorus of boos without a shirt after 7 minutes, it seemed that a retirement was on the cards.
Wawrinka was aggravated during the time out, demanding that officials tell him why Nadal needed the break. And he came out aggressively to finish off the second set.
Nadal's serve speed dipped even further to 125 kph (77 mph) and then 114 kph (70 mph). The support in the stadium gradually shifted as the crowd saw the Spaniard battling to stay on the court.
His service speed improved in the beginning of the third set, reaching 159 kph (98 mph). With Nadal serving at 4-2, a fan yelled "C'mon Stan, no sympathy!"
By the end of the set, Nadal's serve was back up to 174 kph (108 mph) and Wawrinka's error count was escalating.
Just before Nadal served in the sixth game of the fourth set, a chant erupted in the arena, "Ra-Fa, Ra-Fa," lasting until he served the first ball.
But after an exchange of breaks later in the sets, Wawrinka composed himself to serve it out in 2 hours, 21 minutes.
