Novak Djokovic battled through a sore neck to get past Ricardas Berankis in the Western & Southern Open second round on Monday.
Djokovic trailed in both sets before recording a 7-6 (7-2) 6-4 victory over Berankis at the ATP 1000 tournament.
The world number one withdrew from the doubles on Sunday due to neck pain, and the injury seemed to bother the Serbian again.
Djokovic required treatment on his neck numerous times during his win, which marked the first time he was in action on the ATP Tour since the season was suspended in March due to the coronavirus pandemic.
Berankis, a qualifier, managed to break Djokovic three times, but the Lithuanian was never able to consolidate.
Djokovic, the 2018 champion, came from 4-3 down in the first set and trailed 2-0 and 4-2 in the second.
The 17-time grand slam winner improved to 19-0 in 2020 and will face Tennys Sandgren in the last 16.