Cruz led off the fourth inning with a ground-rule double that one-hopped over the right-center-field fence but later was thrown out trying to steal third.
Still, he provided a valuable insurance run in the eighth, opening the inning by taking a 92-mph sinker from right-hander Jerome Williams into the porch above the 404-foot sign in left-center field.
Tillman, despite walking two, hitting two and throwing two wild pitches, allowed just one hit after Dexter Fowler's one-out single in the third.
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“I thought, after the first inning, he reached back and got a little more fastball. ... I can see he gets that little look in his eye, like, ‘Enough of this. Let's go,'” Showalter said. “Very few sequences did he have real good command of the curveball.”
The Astros (24-33) tied the game in the second when Tillman labored through a 24-pitch frame.
He immediately put two base runners on, allowing a leadoff double to Jason Castro and hitting Matt Dominguez with a pitch.
Two batters later, after Chris Davis made a nice diving play on Marc Krauss' grounder for the first out of the inning, a breaking ball slipped out of Tillman's hand and hit Alex Presley to load the bases.
No. 8 hitter Robbie Grossman rolled a breaking ball down the first base line that Tillman chased, waiting for it to roll foul. But it didn't, allowing the Astros to score their first run.
Tillman escaped further damage, getting help from his defense when Markakis — who nearly didn't play Saturday because of a stiff neck — made a tremendous running catch on a ball hit toward the right-field corner by Jose Altuve.
“I wouldn't say it's a relief. It's my job,” Tillman said. “As a starting pitcher, you want to get deep into the ballgame and give your team a chance to win. We were able to do that tonight.”
Orioles right-hander Ryan Webb helped preserve the lead by retiring all four batters he faced before left-hander Zach Britton entered in the ninth and converted his fourth save in five opportunities.
Britton allowed a leadoff single to Dominguez but struck out pinch hitter Jesus Guzman and induced a 6-4-3 double-play ball from pinch hitter Chris Carter to end the game.