Perez did not get a decision on Saturday against Tampa Bay, but was impressive in just his second big league start, as he allowed two runs and five hits in five innings of his team's 6-5 loss. He had allowed just one hit in six scoreless innings in his first start.
The left-handed rookie has faced the O's three times out of the bullpen and has not allowed a run in 2 2/3 innings.
Toronto got a terrific effort from another rookie on Wednesday, as Henderson Alvarez threw eight scoreless innings and earned his first major league win in a 13-0 rout. Alvarez was backed by four home runs and became the youngest Blue Jays starter to win a game since 1979.
"He just pitched a phenomenal game," said Don Wakamatsu, who is filling in while manager John Farrell recovers from pneumonia. "I think it breathes a little life into the offense. We've been swinging the bats better lately."
Former Blue Jay Jo-Jo Reyes (7-11), perhaps best known for the 28-game winless streak he snapped earlier this season, gave up seven hits and eight runs while walking one and striking out two.
"We made a lot of bad pitches. Jo-Jo was pretty flat and didn't have much of an angle going," said Orioles manager Buck Showalter. "But I was impressed with their kid. That goes without saying."
Hoping for a better effort tonight the Orioles will turn to righty Tommy Hunter, who is 3-2 with a 4.98 ERA. Hunter won his second consecutive decision on Friday against New York, as he held the Yankees to four runs and five hits in seven innings.
Hunter is 1-2 with a 6.83 ERA in six games (four starts) against the Blue Jays.
Toronto has won nine of 14 meetings with the Orioles this season.