The new WTA ranking list, published on Monday, saw both players rise 10 places to 40th and 43rd respectively.
Watson is now the highest-ranked Briton since Jo Durie was among the top 30 in 1987, while Robson, who beat former Wimbledon champion Petra Kvitova in Melbourne before losing to eventual semi-finalist Sloane Stephens, continues to track her domestic rival.
Watson has the chance to climb higher this week as she is playing in Pattaya, Thailand.
Victoria Azarenka keeps her top spot thanks to the successful defence of her Australian Open title.
However, she has plenty more points to defend in the next couple of months so looks set to come under more pressure from new world number two Serena Williams and Maria Sharapova.
Beaten Melbourne finalist Li Na is back is up to fifth as a result of her run.