The Rangers carried a 6-2 lead into the ninth and had closer Neftali Feliz on the mound. But Feliz, who's tied for second in the AL with 23 saves, gave up a two-out, two-strike grand slam to Corey Patterson to knot the game at 6.
"We blew an opportunity there," Rangers manager Ron Washington said. "[Feliz] just didn't have it. He just didn't have it.
"He's my closer. I'm shutting the ballgame down. He just didn't get it done. We're not making excuses."
An inning later, reliever Dustin Nippert gave up a leadoff home run to Jake Fox and the O's held on from there.
"This is a big league game. He gave up a home run," Washington said. "It is what it is. I'm not going to sit here and try to excuse it."
The Rangers blew a four-run lead on Thursday in the opening game against the O's, capped by a three-run eighth in which Baltimore scored the tying run after Felix Pie was hit by a pitch.
"It was unbelievable," Orioles interim manager Juan Samuel said. "It was almost the same situation as last night, down four runs. Our bullpen was great and it gave us a chance to come back and get some runs to win the game."
In the first two games of the Rangers' series with the Orioles, the Rangers have raced out to four-run leads after three innings in both games. After that, however, they've been outscored 13-2.
"Both games we had won. Both games the bullpen didn't shut it down," Washington said. "Those are the guys we've been depending on up to this point. They just didn't get it done."
The loss spoiled a strong start from pitcher Scott Feldman, who pitched seven innings while allowing just two runs on eight hits with two strikeouts.
"I think 99 times out of 100, we win that game," Feldman said. "But that's why you play 162 games, and crazy things happen in baseball sometimes. We've probably won some games we shouldn't have one. But on the bright side, we did get Cliff Lee today."
Feldman's success largely came from his ability to pound the strike zone, as the right-hander didn't walk a batter.
"I think I threw the ball a little better tonight," Feldman said. "You always want to get out of here with a win, but you've got to look on the bright side. At least I threw the ball better."
"He was great, he really was," Washington said. "He had his sinker working, he used his off-speed pitches very well tonight. Kept them off balance ... too bad we just couldn't hold on to the game for him."
The Rangers got enough offense to win the game, as Vladimir Guerrero gave the club an early lead with a three-run homer in the third before Joaquin Arias added a run on a bases-loaded walk later in the inning. Josh Hamilton also extended his home hitting streak to 29 games.
They got RBI sacrifice flies in the eighth by Chris Davis -- who had arrived just before the game after Justin Smoak was traded to the Mariners for Lee -- and second baseman Ian Kinsler.
"You hate to lose guys in an organization, but we definitely upgraded in Cliff," Davis said. "For me to come back here and be a part of this, it's pretty special."
But as special as Lee may be as a starter, it's the Rangers' bullpen that's drawn an eye over the last two games.