Weaver allowed a run on three hits over 7 1/3 innings to outduel Wei-Yin Chen, Albert Pujols homered, and the Orioles dropped the opener of the three-game series, 3-1.
"He had command of all his pitches. No real pattern," Orioles manager Buck Showalter said of Weaver. "You see a lot of weak flyball outs. He's usually on top of his game."
J.J. Hardy (2-for-3) homered off Weaver (2-4) to open the eighth and cut the deficit to 2-1, but the Angels added a run in the ninth.
Baltimore couldn't capitalize on Adam Jones' one-out single in the bottom half of the ninth, as Chris Davis flied to the warning track before pinch hitter Travis Snider struck out.
"He's a guy that if you go up there and try to get too aggressive, he uses it against you," Davis said of Weaver. "But at the same time, if you go up there and try to take pitches, you can be behind him. He's throwing the ball well now."
So is Chen (1-2). The Orioles' starter turned in his fourth straight start in which he pitched six or more innings and allowed two earned runs or fewer. He went seven innings against the Angels, allowing two runs on five hits while striking out seven and walking two.
"I thought he had a good breaking ball tonight," Showalter said. "Slider had some late life and bite to it. Commanded the inner half of the plate, which you're going to have to do with that many quality right-handed hitters in the lineup."
Baltimore hitters continue to struggle, as the last-place Orioles are averaging 3.1 runs over their past 13 games.
"We're still looking for that stride where we can -- the nine guys that are in the lineup that day, and maybe a couple of guys coming off the bench -- where we can get rolling four, five, six, seven games in a row and start getting really comfortable" Caleb Joseph said.
There was little comfort to be had against Weaver, who improved to 8-4 with a 3.27 ERA in 13 starts against the Orioles.
Before Hardy's homer, their best chance came when Jones led off the seventh with a bunt single in a 2-0 game, but Weaver got Davis to hit into a 4-6-3 double play.
The Angels' limited success against Chen came early. He retired the first two batters of the game, and then Pujols hit a towering fly to left on 1-2 pitch for his sixth homer of the season.
"It wasn't really a bad pitch, but in that at-bat, I pitched one pitch to the same location, so he already saw a pitch in that location," Chen said through and interpreter. "He made me pay."
In the second, Chen allowed a lead-off double to Erick Aybar, who went to third on a groundout and scored on a sacrifice fly to short right by Carlos Perez.
Harvey Valentine is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.