Tenth seed Novak Djokovic overcame illness and losing the first set to beat Adrian Mannarino in the Cincinnati Masters second round.
The Serbian called for the doctor towards the end of the second set and was given medication for a stomach problem before returning to the court and reeling off six successive games in a 4-6 6-2 6-1 victory.
Having required nine match points to see off Steve Johnson in Monday's first round, the former world number one converted at the first time of asking against Mannarino to advance.
Djokovic is a five-time finalist but the Ohio tournament is the only Masters event he has yet to capture, and he has landed in the favourable half of the draw that does not include Roger Federer.
There were signs that all was not right with Djokovic in the first set when he pushed a series of ground shots long and Mannarino secured the match's first break to go 4-3 up.
The Frenchman then claimed a 6-4 success in the opener with just his second ace.
Djokovic bounced back at the start of the second set by winning Mannarino's first two service games but he then called for medical assistance when he was a game away from levelling the match.
After being given medication at the change of ends, Djokovic looked more like himself in the humidity as he took the second set and then won five consecutive games at the start of the decider.
And, having taken so long to deliver the victory against Johnson, Djokovic was grateful to see Mannarino push his return long on the sole match point.
"I wasn't feeling great for a set and a half, I had some stomach issues," Djokovic said in his on-court interview afterwards.
"The key was overcoming the physical health issue that I had in the first couple of sets.
"I was unable to move that well and I was making a lot of unforced errors."
|Coman back in Bayern training but Lewandowski has knee injury|
|Qalandars land De Villiers in PSL draft, Smith second pick|
|F1 changes helped less talented drivers on the grid - Alonso|
|Agnelli: No super league talks since 2015|
|I hope from now on it only gets better - Floersch update on horror crash|
|Calf injury rules Ashton out of Australia match|
|Halfpenny to miss South Africa clash|
|Hard for Lazio to hold on to Milinkovic-Savic, says Lotito|
|Australia´s next generation pay tribute to retiring Cahill|
|Bairstow pushing hard for Test recall|
|Cane eyes 2019 Super Rugby return after neck break|
|Van Dijk finds time to console referee during Dutch delight|
|Cahill sheds tear at end of phenomenal Australia career|
|WATCH: Pelicans coach Gentry interviews himself|
|Where does Chiefs-Rams classic rank among NFL´s highest-scoring matches?|
|Australia 3 Lebanon 0: Boyle bags brace on Cahill farewell|
|Guendouzi underlines desire to represent France|
|I might need a couple of drinks to relax after that! - Rams coach McVay|
|Juventus´ Alex Sandro has Premier League ambition|
|Ederson taking goalkeeping to another level, says City hero Weaver|
|Ceferin dismisses "super league" plans as fiction|
|Rams defeat Chiefs in one of the highest scoring games in NFL history|
|Kemba Walker leads Hornets to win over Celtics|
|Gomez praises ´top player´ Van Dijk, Stones|
|Cricket Australia to maintain Smith, Warner ball tampering bans|
|Brazil´s Tite encouraged by Neymar captaincy|
|Holmes set for NFL switch after Cronulla release|
|Dier encourages English youngsters to follow Sancho´s lead|
|Southgate promises further changes to England squad|
|Jones sceptical over Pocock injury|
|Sane encouraged despite Germany´s ´annoying´ Nations League draw|
|Character got Netherlands through, says Koeman|
|Netherlands´ focus still on Euros - Van Dijk|
|Ireland will be ready for qualifiers, insists O´Neill|
|Smith undergoes successful surgery, Redskins sign Sanchez|
|Germany 2 Netherlands 2: Dramatic five-minute fightback seals Oranje progression|
|Denmark 0 Republic of Ireland 0: Thrills at a premium again in Aarhus|
|O´Brien could return for start of Six Nations|
|Cavani: Neymar and I are ´friends, brothers, team-mates´|
|Pothas named Windies interim head coach|
|LA Galaxy planning for Ibrahimovic stay|
|NFL will return to Mexico City in 2019|
|Broner vows to end Pacquiao´s career in Las Vegas|
|UEFA should punish PSG and Man City, says LaLiga chief|
|Teenage driver Floersch has ´no fear of paralysis´ after operation|
|Mancini bemoans Italy´s misfortune in front of goal|
|Sprint legend Johnson ´pretty much back to normal´ after stroke|
|Bournemouth defender Adam Smith out for three months|
|World champions France out to end 2018 on a high|
|I told him there´s no future in football! A-Rod relieved to be ignored by Mahomes|
|Dembele must focus and be more responsible - Suarez|
|Neymar could return one day – Barca chief|
|Cole backs West Ham to keep Arnautovic|
|Injury rules Bernardo Silva out of Poland clash|
|Lamar Jackson debut start ´spectacular´ - Ravens coach Harbaugh|
|Babar run out the turning point, laments Sarfraz|
|West Ham boost London Stadium capacity to 60,000|
|A great advertisement for Test cricket - Williamson revels in stunning win|
|Van Dijk one of the world´s best - Klaassen|
|Floersch had ´angel on her shoulder´ in horror crash|
|Gascoigne charged with sexual assault|
|I am going to stay at Chelsea and fight, insists Giroud|
|Hansen to make announcement on All Blacks future|
|I have reached the top by joining Chelsea - Sarri|
|Bonucci tells Italy boo boys to ´live with less envy´|
|Dramatic Pakistan collapse gives Stead first New Zealand Test win|
|Button enjoying racing for first time in years|
|Dortmund chief not planning Pulisic sale|
|Theismann: Smith leg break ´heart-wrenching´ to watch|
|Wolves defender Jonny suffers knee injury|