NASHVILLE, Tenn. -- Pucks just keep going in for Alexander Steen.
Nick Spaling scored for Nashville, which has lost two of three as it sets out on a season-long seven-game road trip.
St. Louis has won four straight in Nashville for the first time.
"I thought we played really well, but it was a strange game," St. Louis coach Ken Hitchcock said. "For the two teams that play each other, we don't give up many of scoring chances and they don't give up many, but there seemed to be a lot of scoring chances."
Steen scored the game's first goal at 5:27 of the opening period.
With the Blues on a power play, Steen beat Nashville goaltender Carter Hutton with a wrist shot from above the left faceoff dot. A screen from teammate Chris Stewart helped Steen score his ninth of the season.
"There's no way that goes in, too far out to beat him with a wrister unless (Stewart) takes away his eyes," Steen said. "I thought we had good jump and we got out of the gates a lot quicker than we did last night."
He has at least one goal in all but one of St. Louis' games this season.
Oshie and Schwartz scored 4:02 apart in the second period to send the Blues into the second intermission up 3-0.
Spaling got the Predators on the board with a short-handed goal less than a minute into the third when he scored his first goal of the season on breakaway, beating St. Louis goaltender Jaroslav Halak on the stick side.
"We were feeling good in here and we had a lot of momentum off those first couple of periods," Oshie said. "I think we responded really well even though giving up short-handed goals is a tough act to follow."
The Blues put the game out of reach after Steen scored his second of the game at 4:37 and Roy followed at 7:48.
Steen already has surpassed his goal total from the lockout-shortened 2012-13 season, when he had eight in 40 games.
"From us, we need a little more production from our forwards," Nashville coach Barry Trotz said. "When we get a chance to convert, we've got to convert."
Hutton was lifted following Roy's goal. He was replaced by Magnus Hellberg, who was recalled Thursday after No. 1 goaltender Pekka Rinne had surgery to clear up an infection in the hip that he had surgically repaired in the offseason.
Pietrangelo added a power-play goal at 12:58 of the third.
"They're a shooting power-play; we knew that's what they were going to do," Nashville captain Shea Weber said. "They get pucks through with traffic. They have a great power play and they scored enough tonight."
Roy played in his 600th career NHL game. ... Blues LW Magnus Paajarvi sustained an upper-body injury in the first period and did not return to the game. ... Before Saturday, Nashville had gone seven games without allowing a power-play goal. .. Predators D Mattias Ekholm recorded an assist on Spaling's goal, his first career NHL point.