Melbourne - Novak Djokovic sought a medical timeout for a lower back injury as he claimed his 11th round of 16 appearance at the Australian Open on Saturday.
The six-time champion advanced with a clear-cut 6-2, 6-3, 6-3 win over Spanish 21st seed Albert Ramos-Vinolas in 2 hours and 21 minutes on Margaret Court Arena.
But there was concern in his camp when the former world No 1 sought a medical timeout early in the second set for treatment to his lower back.
Djokovic later played down the extent of the problem, saying "it's okay, nothing major".
The Serb, looking for matches after a six-month lay-off with right elbow trouble, will face South Korea's Chung Hyeon in Sunday's fourth round after he shocked fourth seed Alexander Zverev.
The injury was a fresh worry for the 12-time Grand Slam champion, whose ranking has slipped to 14 after an inactive second half of 2017.
"It's okay. Nothing major. I knew I wanted to use the medical timeout because I needed it," he said.
"But at the same time I knew it was nothing major that can potentially raise a question mark on whether I can continue playing or not. It was fine.
"Look, I haven't played for six months. We have to take that in consideration.
"I played a long match against Gael Monfils a few days ago. I have maybe some tensions in the muscles or whatever, some kind of physical challenges.
"It's nothing major to be concerned about. I'll deal with it. It's fine."
Djokovic, who was upset by Denis Istomin in the second round of last year's tournament, was workmanlike as he broke the Spaniard's serve five times, although his errors outnumbered his winners 40-37.
It took his record against Ramos-Vinolas to 5-0 with two of the wins at Slams.
"It was 2 hours, 20 minutes, straight-sets win, but I had to earn it," he said.
"I worked hard on the court. Ramos-Vinolas doesn't hand you the win. He makes you earn it.
"It was great for me to actually get into those long exchanges and rallies, to get some rhythm on the court after the Gael Monfils match, which was really up and down.
"I am very pleased where my game is at. I know that matches from this moment onwards will get tougher and tougher."
Should Djokovic beat Chung he is facing a potential quarter-final against Austria's fifth seed Dominic Thiem, who must first get past American surprise packet Tennys Sandgren on Monday.
Collated results from the Australian Open on Saturday:
Dominic Thiem (AUT x5) bt Adrian Mannarino (FRA x26) 6-4, 6-2, 7-5
Tennys Sandgren (USA) bt Maximilian Marterer (GER) 5-7, 6-3, 7-5, 7-6 (7/5)
Marton Fucsovics (HUN) bt Nicolas Kicker (ARG) 6-3, 6-3, 6-2
Fabio Fognini (ITA x25) bt Julien Benneteau (FRA) 3-6, 6-2, 6-1, 4-6, 6-3
Chung Hyeon (KOR) bt Alexander Zverev (GER x4) 5-7, 7-6 (7/3), 2-6, 6-3, 6-0
Tomas Berdych (CZE x19) bt Juan Martin Del Potro (ARG x12) 6-3, 6-3, 6-2
Novak Djokovic (SRB x14) bt Albert Ramos (ESP x21) 6-2, 6-3, 6-3
Roger Federer (SUI x2) bt Richard Gasquet (FRA x29) 6-2, 7-5, 6-4
Karolina Pliskova (CZE x6) bt Lucie Safarova (CZE x29) 7-6 (8/6), 7-5
Madison Keys (USA x17) bt Ana Bogdan (ROM) 6-3, 6-4
Simona Halep (ROM x1) bt Lauren Davis (USA) 4-6, 6-4, 15-13
Caroline Garcia (FRA x8) bt Aliaksandra Sasnovich (BLR) 6-3, 5-7, 6-2
Naomi Osaka (JPN) bt Ashleigh Barty (AUS x18) 6-4, 6-2
Barbora Strycova (CZE x20) bt Bernarda Pera (USA) 6-2, 6-2
Angelique Kerber (GER x21) bt Maria Sharapova (RUS) 6-1, 6-3
Hsieh Su-wei TPE) bt Agnieszka Radwanska (POL x26) 6-2, 7-5