Martina Navratilova was the only WTA player to simultaneously win her first Grand Slam and become number one for the first time

I found one case in WTA history where a player simultaneously won her first Grand Slam title and became number one for the first time: at Wimbledon in 1978, second-ranked Martina Navratilova did so, defeating top-ranked Chris Evert to  claim the number-one ranking. At Wimbledon in 2002, second-ranked Serena Williams defeated top-ranked Venus Williams to become number one for the first time – but that was already her third Grand Slam title. And in a third case, which the Australian Open tweeted about, second-ranked Caroline Wozniacki defeated top-ranked Simona Halep there in 2018 in a battle for number one and a first Grand Slam title – but both had been number one before. (Andrew Shields, #111words, 11 September 2022)