Patrick Mouratoglou has steered Serena Williams to some of her greatest achievements, but the coach has never seen the American work as hard as she has to battle back from injury and illness in pursuit of a record-equalling 24th Grand Slam singles title.
Williams will face unseeded late-bloomer Barbora Strycova on Thursday for a place in the Wimbledon final, having begun the tournament short on match practice and with question marks hanging over her prospects.
The 37-year-old had barely played since the Australian Open in January after a niggling knee injury limited her court time and the rust was all too visible as she began her campaign at the All England Club.
Margaret Court's record 24 slams has dominated Williams' late career, especially after she returned to the sport following the birth of her daughter in 2017 when she suffered a pulmonary embolism that left her bedridden for six weeks.
"Twenty-four will mean that she will equal the record of all time... and that's why she came back to playing tennis after having a baby and so many medical complications. The effort she has put in, I have never seen something like this," Mouratoglou told reporters on Wednesday.
"You have no idea how much she worked, how hard she worked to come back to that level and she came back for that (record) so it will probably mean a lot if she makes it."
In the run-up to Wimbledon, however, injuries and illness had limited Williams to just seven matches since the Australian Open in January.
According to Mouratoglou, Williams has been playing without any pain for three weeks and is feeling "so much lighter" in spirit -- an ominous warning to Strycova, who has played the American on three occasions and lost every time.
"She is in a good place at the moment, she is happy, has a house, her husband is here her daughter is here and she is pain free," he said.
"In the last match you could see that she has been able to raise her level when it was necessary, which is one of her trademarks and this is back so everything is positive."