It was a returner's delight for the first half of the match - the first eight games of the match were all breaks of serve, Begu and Niculescu always with their nose in front, 1-0, 2-1, 3-2 then 4-3.
But after breaking back for 4-all, Hingis and Mirza never lost serve again - and broke their Romanian opponents three more times - to advance to the quarterfinals after an hour and three minutes.
The Swiss-Indian duo is now 16-2 since first joining forces at the beginning of March, winning Indian Wells, Miami and Charleston but falling earlier than they would have hoped at Stuttgart and Miami.
Awaiting in the quarters are Julia Goerges and Sílvia Soler-Espinosa, who rallied from 4-2 down in the first set and 5-3 down in the second to beat Anna-Lena Groenefeld and Alexandra Panova, 6-4, 7-6(1).
If this tweet is anything to go by, the German-Russian pairing were pretty happy with the win:
? Silvia Soler (@solerespinosa) May 12, 2015