Yambatis (3-3) scattered four hits while also walking four.
Offensively, Sean Reilly and Liam Hicks each had two hits and a run. Josh Garton drove in two, and Brendan Keys added an RBI.
Guelph improved to 10-19.
Keegan Marsden had two hits for Kitchener, which dropped to 19-9.
Jonder Martinez (4-2) took the loss, giving up three runs on nine hits with eight strikeouts over 7.1 innings.