Sakkari had no issues against Ons Jabeur, cruising through to the final-four with a 6-2 6-3 victory.
The Greek needed only 69 minutes to dispatch the world number two, having previously accounted for Aryna Sabalenka and Jessica Pegula in the Nancy Richey Group.
Sakkari took advantage of some wastefulness from Jabeur, with the Tunisian posting 19 unforced errors with just eight errors.
Her efficiency did not improve in the second set, managing only three winners with 12 unforced errors.
Sakkari's serve was a weapon throughout, landing 70 per cent of her first-serves fair and converting 82 per cent of those chances (27-of-33) into points.
Jabeur could have advanced through to the next round with a win but instead Aryna Sabalenka will advance with Sakkari to the final four after the Belarusian defeated Pegula 6-3 7-5.
The only other player yet to lose a set in the tournament is Iga Swiatek in the Tracy Austin Group – although the top-ranked- Pole has only played two matches so far.