David Perron scored for the fifth straight game, and Ville Husso made 43 saves for St. Louis (34-17-9), which has lost six of eight (2-3-3).
"We'll take any points we can get, but at the same time, that wasn't our best effort," Blues forward Brandon Saad said. "It's good to get a point, but it's something we need to correct."
Ruhwedel gave the Penguins a 1-0 lead at 14:42 of the first period, scoring on a one-timer from the blue line through traffic following an offensive zone face-off win.
Pittsburgh helped itself by killing off a 5-on-3 Blues power-play for 1:34, which began in the first minute of the game.
"That was huge," Rust said. "Things could go south very quickly if we don't get it done there. Everyone did a good job. Jarry made some big saves. Kind of from there, we just gained momentum. I think we were pretty good from there throughout the whole game."
Matheson made it 2-0 at 10:52 of the second period on a wrist shot from the left face-off dot to the glove side of Husso.
"I think we did a good job of being up all night and controlling the momentum by having our 'D' up in the zone and keeping pucks alive," Matheson said. "That's when we're at our best. It allowed our forwards to wear down their 'D' and allowed us to play our game."