Novak Djokovic admitted he had to “fight” to come back from a set down to beat world number 36, Hungary’s Marton Fucsovics at the Qatar Open on Wednesday.
The world number one survived a huge scare to eventually triumph 4-6, 6-4, 6-1.
“For the first two sets he was the better player,” said Djokovic.
“He played really well, smart, changing up the rhythm and the pace of the ball and moving me around.
“I was kind of in a corner and I had to find my way and fight my way through.”
The match lasted exactly two hours, which was twice as long as the Serb spent on court in his first round stroll against Damir Dzumhur, where he lost just three games.
A backhand winner eventually secured victory for Djokovic but the result was in doubt for a long time, with the Serb only breaking Fucsovics in the tenth game of the second set to ensure the match went into a final set shootout.
Djokovic will play either Russia’s Andrey Rublev or Nikoloz Basilashvili of Georgia in the quarter-finals.
That pair play later on Wednesday.
If he wins his last eight match, Djokovic is on course to meet Stan Wawrinka in the semi-finals after the Swiss also won on Wednesday, beating Chile’s Nicolas Jarry 6-4, 7-6 (7/3).