Hewitt progresses in Halle
The Australian, defending his crown in Germany, will now face home favourite Philipp Kohlschreiber in the last eight after he overcame Alexandr Dolgopolov 6-3 7-6.
"Obviously Kohlschreiber is a quality player, who has come far in this tournament so I have to watch out," said Hewitt.
"I'd like to execute my game like I did today, that would be great."
Gael Monfils, seeded three in Halle, also cruised into the quarter-finals with a 6-2 6-3 victory over Ivan Dodig of Croatia.
Next for the Frenchman is a match against another home player, Florian Mayer, who beat Yen-Hsun Lu 7-6 3-6 6-4.
In the remaining quarter-final Milos Raonic will play Philipp Petzschner.