Grebenchuk's career briefly flourished in 1989 and 1990. She emerged as a fast runner in her mid-twenties after running a best of 1:57.89 minutes in 1987 (ranked twelfth globally) and then 1.58.70 minutes in 1988 (ranked 25th). Her first and only national title came at the 1989 Soviet Indoor Athletics Championships, where she topped the podium in 2:02.62 minutes. International success followed: the 1989 European Athletics Indoor Championships saw her place third in the 800 m behind Romania's Doina Melinte and East Germany's Ellen Kiessling. Shortly after she entered the 1989 IAAF World Indoor Championships and retained her good form by running a lifetime indoor best of 1:59.53 minutes. This was enough to hold off Kiessling for the silver medal, as she finished second behind East German Christine Wachtel. The time ranked her as the second fastest athlete indoors that year.