And Johnson was again tested physically and mentally in his second round match from which he eventually emerged a 6-2, 7-6 (8), 3-6, 7-6 (6) victor.
For almost 4 full hours Wednesday, Johnson stayed the course, over and over, even as the on-court particulars grew complicated. The young Croatian was booed while leaving the court but it bears remembering - an equally frustrated Johnson smashed his racquet earlier in the match, an event which laid the groundwork for the point penalty assessed after he casually flicked away a ball after a Coric victor.
In a match that saw tempers fray at both ends, Croatia's Coric repeatedly smashed his racquet into the court after losing the fourth set, having held set points.
Only when, on his fifth chance to end things, Johnson delivered a clean forehand victor to seal the victory, did he let go, dropping onto to his knees near the baseline, his chest heaving, his eyes filling with tears.
Johnson, who won a five-set match Monday, advances to a third-round match against Dominic Thiem, the No. 6 seed.
Though still in the early stages of the grieving process, Johnson was able to gut out his emotional first-round win and then somehow held on through Wednesday's match, immediately falling to his knees and breaking down into tears after slapping a forehand victor on match point. A long match. Up and down.
"I knew he was looking down on me in that last point and it gave me the strength to finish it off".
'I just miss my dad I wish he was following along - I know he is from upstairs, ' he said after the win against Borna Coric.More news: Samsung has a 6GB Galaxy S8+ to boost sales in India
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"Super tough, definitely", the 40th-ranked Croatian said.
"All the credit to him that he was able to go through this period and also to play this good".
Rafael Nadal and Novak Djokovic had the pulses racing on the show courts at Roland Garros on Wednesday, but it was on Court 6 where the heart strings were tugged.
After they shook hands, Johnson leaned his head on his arm atop the net, sobbing.
Johnson's dad, Steve Sr, passed away suddenly in his sleep on May 11 at the age of 58 - something that the 27-year-old is still, understandably, coming to terms with. She graduated college and, you know, they were going to come here and kind of follow me to Queens and then go back before she starts work and whatnot. Who knows how long it'll take? "He raised me to be a competitor and a fighter until the last point. may not be the best tennis player but I will always fight".
"Probably one of the harder matches I've played".
There were other winners and losers, of course, on Day 4 of the French Open, but nothing quite so poignant.