Simon, originally given a three-game suspension after a run-in last weekend against Toronto, had the penalty cut to two on Wednesday.
The right-hander started serving the suspenion Wednesday night
Simon was also fined an undisclosed amount by Major League Baseball after home run leader Jose Bautista of the Blue Jays was plunked Sunday following a warning by the umpires.
Baltimore starter Rick VandenHurk hit Bautista, who has nine homers against the Orioles, in the third inning and both benches were warned after Toronto's Shaun Marcum hit designated hitter Luke Scott to begin the fourth.
Simon replaced VandenHurk to begin the fifth. With one out, the first two pitches to Bautista were balls -- the second of which was high and tight -- and Simon then hit the Toronto star on the left forearm and was ejected by plate umpire Bill Welke.
Orioles manager Buck Showalter said the incident was unintentional.