WATCH: Djokovic fakes it for next opponent Nishikori

Novak Djokovic doesn't like to give his opponents an edge—ever. The world No. 1 endured some struggles to take out world No. 19 Daniil Medvedev, 6-4, 6-7 (5), 6-2, 6-3 in 3 hours and 15 minutes.

In the on-court interview, the Serbian was all smiles and made sure to send a message of perfect health to his next challenge, Kei Nishikori.

"Since I guess my opponent is watching: I'm feeling fantastic. I've never been fresher in my life," Djokovic said.

He wasn't sure who he'd be facing since his match finished after midnight, while Nishikori wrapped up his win over an hour earlier. In press, the 31-year-old Djokovic told the truth.

"I didn't feel so great, you know, in the last 20 minutes of the match or so," Djokovic said. "It was not the fall. It was not particularly the fall [in the third set]. It was just, you know, a little bit of fatigue, a little bit of back. Nothing major."

Nishikori should be feeling a little more worse for wear when they face off in the quarterfinals. He survived a five-hour epic fifth-set tiebreak win over Pablo Carreno Busta, marking his third match this tournament that's gone the distance.

Kickoff each day of the 2019 Australian Open with Tennis Channel Live, reviewing the day's most important news and previewing the day's biggest matches. Watch LIVE at 6 p.m. ET.

Follow the Australian Open even closer with Tennis Channel PLUS. Go to BuyTCPlus.com and subscribe now!