Iga Swiatek survived a major scare as she came from a set and a break down to beat Jule Niemeier and set up a US Open quarter-final with Jessica Pegula.
The world number one looked to be in a real spot of bother against the German ranked 107 places below her, but Niemeier could not maintain her blistering start and Swiatek claimed a 2-6 6-4 6-0 victory.
Swiatek initially looked a shadow of the player who had not lost a set in the first week, with Niemeier's power and unpredictability causing the Pole no end of issues.
Niemeier was immediately a break up and had no problem consolidating before eventually getting another to lead 5-2.
So underwhelming was Swiatek that Niemeier could even afford three double-faults in the final game of the opener as the German impressively took a first-set lead.
After a bathroom break, Swiatek returned with greater purpose but was still lacking ruthlessness; she inexplicably missed a forehand on break point at 1-0 up in the second, and then she stuck a simple volley into the net a few minutes later to find herself a break down.
That was the first of seven breaks in a second set defined by poor serving, but Swiatek was just slightly better than her opponent, with successive breaks giving her the edge in a rollercoaster encounter.
From there, Niemeier barely registered as a threat due to her wastefulness, recording four double-faults and 14 unforced errors to Swiatek's zero and one respectively in the decider as the latter bageled her opponent.