American Sloane Stephens gave an indication of her French Open ambitions, defeating No.18 Karolina Muchova of the Czech Republic 6-3, 7-5 in one hour, 55 minutes to move into the pre-quarterfinals on Saturday.
The 2018 runner-up will next face another Czech player, world No.33 Barbora Krejcikova, who had won her maiden title in Strasbourg last week to signal her intent.
Barbora extended her winning streak to eight, thrashing No.6 seed Elina Svitolina of Ukraine 6-3, 6-2.
Karolina and Elina's exit means the only seeds remaining in the top quarter of the draw are No.13 Jennifer Brady, No.24 Coco Gauff (both US) and No.25 Ons Jabeur (Tunisia).
Sloane, who has now reached the fourth round on seven of her 10 appearances at Roland Garros, was in control of the proceedings from the start, taking a 6-3, 2-0 lead.
The world No. 59 American got 84 per cent of her first serves in and, combining it with aggressive play, left Karolina clueless.
Though Karolina did come up with occasional winners, the Czech player was unable to consistently trouble Sloane.
"My first big fourth round or whatever at a slam was here," said Stephens. "And obviously consistently making fourth round here has been kind of a staple for me, which has been great. Obviously one of my favourite tournaments of the year, so peaking here has always been really important."
The 25-year-old Barbora Krejcikova, a former doubles world No. 1 who won the French Open title partnering country-mate Katerina Siniakova in 2018, had also reached the fourth round here last year to break into the top 100. Since then, her career has been on the upswing and last week she captured her maiden title in Strasbourg.
On Saturday, Barbora simply blew away the No.6 seed Elina with her carefully-disguised shots, which fetched her 38 winners in the match.
