Keothavong moved up seven places to 121 in the latest rankings
Britain's Anne Keothavong beat Kristina Barrois of Germany in the first round of the Cellular South Cup in Memphis.
The Londoner, 26, eased past the sixth seed 6-1 6-3 in the opening match of her second tournament back after a six-month injury lay-off.
Keothavong goes on to face Portuguese teenager Michelle Larcher de Brito.
Russian top seed Maria Sharapova dismantled Shenay Perry 6-0 6-2 in the opening round to record her first victory on tour this year.
The former world number one needed just 51 minutes to dispatch her American opponent, breaking Perry's service six times.
She will play American Bethanie Mattek-Sands in the next round.
Sharapova was coming off a disappointing performance at the Australian Open last month when she fell in the first round to compatriot Maria Kirilenko.
British number one Elena Baltacha, ranked 70th in the world after last week's Michigan ITF title win, will play Renata Voracova from the Czech Republic in round one.
Keothavong, currently ranked 121, is making her way back from a serious knee injury and has plenty of points to defend in Memphis having reached the semi-finals last year.
The victory over Barrois, the world number 71, also avenged a defeat in their only previous meeting four years ago.
'I surprised myself today with how well I played and it's great to know my level is there against a top hundred ranked player," Keothavong told her website.
"Kristina is an awkward opponent who mixes it up very well but I was so focused and stuck to my game plan. My serving isn't quite where I want it to be but saying that, I didn't drop serve once today."
Keothavong broke serve at the first opportunity and went on to dominate the first set, closing it out after a lengthy seventh game.
And she grabbed the crucial break in game six of the second set before wrapping up victory after one hour 18 minutes.