The 37-year-old American stormed past top seed Simona Halep to reach the quarter-finals at the Australian Open on Monday, with the Romanian saying it felt like being “hit by a train”.
Long-time coach Mouratoglou said Williams was in a different space to the one she occupied at Flushing Meadows, when she controversially lost the decider to Naomi Osaka during her comeback from having a baby.
In that match, Williams lost the plot, receiving a code violation for coaching, a penalty point for racquet abuse and a game penalty for calling the umpire a “liar” and a “thief”.
Mouratoglou admitted “I don’t think she was ready” to win a final back then.
“There is a big difference between reaching a final and winning it,” he added.
But four months on from that chapter of her life that Williams now refuses to talk about, he said she was “back to being Serena”.
“I think she’s fitter than she was last year, because even though she made really a lot of efforts to come back in shape last year, I don’t think she had enough time,” he said.
“Having a baby is a big thing. So for a top-level athlete to come back and be 100 percent fit after having a baby any time, I think there was not enough time.
“So I think now she’s ready physically. I think emotionally too because it’s a big change in anyone’s life to have a baby and you need to get used to a new life, and it took a bit of time.
“But I feel now she’s back to being Serena on both the physical and emotional side. So I think her level is good. I think she needed a big fight, and it happened (against Halep) and I think it’s a great thing,” he added.
Williams, seeded just 16, beat world number one Halep 6-1, 4-6, 6-4, repelling a gutsy fightback from the Romanian after blitzing her in the first set.
She next plays seventh seed Karolina Pliskova for a place in the semi-finals, where she could meet either Osaka or sixth seed Elina Svitolina.
Asked if the 37-year-old could go on and win her eighth title in Melbourne to match Court’s long-standing record, Mouratoglou replied: “Of course I believe she will win.
“First of all, I always think she can win, and she will win. I think I should be in that state of mind. Because she’s Serena.”