Southern Illinois (3-3) pounded out 14 hits in a 9-0 home-field shellacking of WIU (0-5).
Whitmer (2-0) scattered four hits across eight innings with a career-high 12 strikeouts and no walks. He lowered his ERA to 0.64.
"[Whitmer] just filled it up, man," coach Ken Henderson said. "He throws strikes. He changes speeds. He has command of every pitch. That was about as dominant a performance as we've seen on the bump in a few years."
The last SIU pitcher to throw eight shutout innings was Aaron Hauge, who held Illinois scoreless on seven hits with six strikeouts and two walks in a win at Champaign on March 15, 2015.