For the first time in the last few years, an established top 4, with momentum on their side with nothing to prove, will kick off a women’s singles Grand Slam at the Australian Open on Sunday but the likelihood of a major upset in some feisty early rounds looms large. The reason: the unpredictable level of Major champions of the past making their comebacks. Iga Swiatek, Aryna Sabalenka, Elena Rybakina, and Coco Gauff each have a Major under their belt and come into the first Slam of the year with confidence-boosting wins during the tune-up tournaments in Australia. But it is the progress of the returning mothers that remains the dominant storyline of the women’s section of the tournament. Former champions Naomi Osaka and Angelique Kerber are chief among them. Caroline Wozniacki, who reached the fourth round at the US Open last year, three years on from initial retirement; and Elina Svitolina, still representing an embattled Ukraine after reaching the semi final at Wimbledon six months after childbirth; are stories that will continue to draw …