Raonic, the big-serving Canadian youngster, saw off Germany's Philipp Petzschner 7-5 7-6 (7/1) in a match containing only one break point, and in which the fifth seed fired a fearsome 19 aces.
Kohlschreiber saw off Jamaica-born fellow German Dustin Brown in successive tie-breaks. A first set containing one break apiece ended with the eighth seed winning the breaker 7/4 and he repeated that scoreline in the second.
He next faces Lukasz Kubot after the Pole overcame Jarkko Nieminen 6-4 6-4.
Ze Zhang awaits Raonic after springing a surprise against Tobais Kamke, the Chinese qualifier winning 6-4 7-6 (7/2).
Russia's Mikhail Youzhny was a 6-3 6-2 winner over Robin Haase of Holland while Cedric-Marcel Stebe beat Carlos Berlocq in the only three-set match of the day, 6-3 3-6 7-5.