PHILADELPHIA -- It was perhaps fitting that Colton Cowser -- a player who didn't start the game -- made arguably the two biggest plays in the Orioles' wild 3-2 series-opening victory over the Phillies on Monday night.

That's just the kind of night it was as the Orioles pulled out yet another one-run victory in front of a sold-out crowd -- one that featured plenty of Baltimore fans -- at Citizens Bank Park.

For starters, the Orioles were coming off a taxing four-game series victory over the Rays in which they took sole possession of first place in the American League East. On top of that, each of Baltimore’s top three high-leverage relievers was unavailable Monday. And if that weren’t enough, Phillies starter Cristopher Sánchez had a career game on the mound.

Making matters worse, the Orioles lost center fielder Aaron Hicks in the third inning when he sustained a left hamstring injury on a diving catch -- and replay later showed that he actually dropped the ball. It balanced out in the fifth when Anthony Santander thought he made a diving catch to rob Jake Cave, but the umpires ruled he trapped it -- and replay was inconclusive.

The night also featured Jordan Westburg’s first career home run, an ejection (of Phillies shortstop Trea Turner) and the Orioles throwing out the potential go-ahead run at the plate on the same play that the tying run scored in the eighth.

“I feel like we play quite a bit of these types of games, so our guys are used to craziness in the last few innings,” said manager Brandon Hyde, whose club improved to an AL-best 19-9 in one-run games. “We don't really blow people out, and we don't get blown out very often. Usually, the games are tight.”

That was certainly the case Monday, when Dean Kremer held the Phillies to just one run over seven innings to outduel Sánchez, who had a career-high eight strikeouts over seven innings of two-run ball. Those runs came on solo homers by Westburg and a Statcast-projected 451-foot shot by Ryan Mountcastle.

And with both Yennier Cano and Félix Bautista unavailable after pitching four of the past five days (including two straight), Kremer’s bounceback gem could not have come at a better time.

“It makes it easier to sleep -- still not easy to sleep, but yeah,” said Kremer, who allowed five runs over 4 2/3 innings Wednesday against the Dodgers. “Just trying to give the bullpen a break. They did an incredible job in [St. Petersburg] this past series, and we're just looking to pick them up.”

With Mike Baumann also getting the night off in addition to Baltimore's star relief duo, Hyde turned to Danny Coulombe with a one-run lead in the eighth. Then, with two on and two out, Bryan Baker entered to face Nick Castellanos, who lined a single to left-center field.

Cowser raced into the gap to field the ball, then fired a throw to shortstop Jorge Mateo, who relayed it to the plate. With Kyle Schwarber having already scored the tying run, catcher James McCann corralled the off-target throw and dived back across home to tag Bryce Harper a moment before he slapped the plate.

“When the ball was hit to my right, I was really just trying to get something in that Jorge could handle, and he made a great pick -- I kind of short-hopped him,” Cowser said. “It ended up being a really close play, but I'm glad we got him.”

Cowser quickly followed his first career outfield assist with his first career extra-base hit -- a go-ahead RBI double in the top of the ninth off Phillies closer Craig Kimbrel.

“Like we talk about a lot, it's somebody different every night,” Hyde said. “And tonight, it was a few different guys.”

Even with Cowser promptly restoring the Orioles’ one-run lead, Hyde once again had to find an alternative for the final three outs.

Hyde opted to go with left-hander Cionel Pérez, who recorded two quick outs before allowing a hard-hit single to pinch-hitter Alec Bohm that deflected off Mateo. Pérez walked pinch-hitter J.T. Realmuto to put the potential winning run on base, but the southpaw escaped by getting Johan Rojas to ground into a forceout.

The result was Pérez notching his second career save -- and his first of 2023. On a night when Westburg and Cowser recorded firsts of their own, it was just the latest example of the resilience of an Orioles team eyeing its first postseason appearance since 2016 -- and its first pennant since 1983.

“If we want to go where we want to go, we've got to have other guys step up and be able to pitch in those kinds of situations,” Hyde said. “We can't pitch Cano and Bautista every single night. And Pérez got through it tonight.”